diff --git a/periscope/src/backend/periscopex/finding_engine.py b/periscope/src/backend/periscopex/finding_engine.py
index c385d2f..a7c2077 100644
--- a/periscope/src/backend/periscopex/finding_engine.py
+++ b/periscope/src/backend/periscopex/finding_engine.py
@@ -300,6 +300,10 @@ def _seed() -> None:
          requirement="L1 grouping (DQ/DQS / byte-lane) cannot be reconstructed — not PASS.")
     _add("PE-PRT-L1-003", "MANDATORY", "RULE", domain="pcb",
          requirement="L1 geometric length/via vs NUMERIC or DESIGN millimetre limit.")
+    _add("PE-PRT-L2-001", "TYPICAL", "REVIEW", domain="pcb",
+         requirement="L2 electrical skip: Z/termination/levels need datasheet/stackup/fab/cited pack.")
+    _add("PE-PRT-L2-002", "MANDATORY", "RULE", domain="pcb",
+         requirement="L2 Z/termination vs cited pack or PHY datasheet window.")
 
 
 _seed()
diff --git a/periscope/src/backend/periscopex/protocol_l0.py b/periscope/src/backend/periscopex/protocol_l0.py
index f0ef665..8f9fd56 100644
--- a/periscope/src/backend/periscopex/protocol_l0.py
+++ b/periscope/src/backend/periscopex/protocol_l0.py
@@ -296,11 +296,14 @@ def protocol_exam(
     graph: DesignGraph | None,
     catalog: ProtocolCatalog | None = None,
     layout: LayoutGraph | None = None,
+    constraints_map: dict | None = None,
+    impedance_nets: list[dict] | dict | None = None,
 ) -> tuple[ProtocolCertificationSection, list[Finding]]:
-    from backend.periscopex.protocol_l1 import (
-        PACK_MACROPHASE as L1_MACRO,
-        LEVEL as L1_LEVEL,
-        certify_l1,
+    from backend.periscopex.protocol_l1 import certify_l1
+    from backend.periscopex.protocol_l2 import (
+        PACK_MACROPHASE as L2_MACRO,
+        LEVEL as L2_LEVEL,
+        certify_l2,
     )
 
     if graph is None:
@@ -309,22 +312,30 @@ def protocol_exam(
     instances = recognize_physical_buses(graph, cat)
     if not instances:
         sec = empty_protocol_section()
-        sec.macrophase = L1_MACRO
+        sec.macrophase = L2_MACRO
         return sec, []
     l0, findings = certify_l0(graph, instances, cat)
     l1, l1_findings_out = certify_l1(graph, instances, layout, cat)
     findings.extend(l1_findings_out)
+    l2, l2_findings_out = certify_l2(
+        graph, instances, cat,
+        layout=layout,
+        constraints_map=constraints_map,
+        impedance_nets=impedance_nets,
+    )
+    findings.extend(l2_findings_out)
     dumps: list[dict[str, Any]] = []
     for inst in instances:
         row = inst.model_dump()
         row["l0_checks"] = [c.model_dump() for c in l0.get(inst.instance_id, [])]
         row["l1_checks"] = [c.model_dump() for c in l1.get(inst.instance_id, [])]
+        row["l2_checks"] = [c.model_dump() for c in l2.get(inst.instance_id, [])]
         dumps.append(row)
     sec = ProtocolCertificationSection(
         schema_version=SCHEMA_VERSION,
-        macrophase=L1_MACRO,
+        macrophase=L2_MACRO,
         recognized_instances=dumps,
         message="",
-        max_level_reached=L1_LEVEL,
+        max_level_reached=L2_LEVEL,
     )
     return sec, findings
diff --git a/periscope/src/backend/periscopex/protocol_l2.py b/periscope/src/backend/periscopex/protocol_l2.py
new file mode 100644
index 0000000..30f9af1
--- /dev/null
+++ b/periscope/src/backend/periscopex/protocol_l2.py
@@ -0,0 +1,624 @@
+"""M4: L2 ELECTRICAL protocol certifier. Z, termination, levels, rise/fall.
+
+Z only from datasheet / stackup / fabricator / cited pack — never invented
+90 Ω USB. USB-IF/IEEE numbers only if the pack has a cite. Silicon cross is
+max PCB × PHY subset when datasheet windows exist. Length is not delay.
+Not L3 / OpenEMS. L0/L1 are not electrical certification.
+RECOMMENDED never FAIL. MISSING_SOURCE / UNKNOWN when cite is absent.
+Visible skip (PE-AF-002 style) when Z cannot be obtained.
+"""
+
+from __future__ import annotations
+
+from typing import Any, Literal
+
+from pydantic import BaseModel, Field
+
+from backend.periscopex.constraints_lookup import match_constraints
+from backend.periscopex.finding_engine import complete_finding
+from backend.periscopex.models import (
+    ComponentConstraints,
+    ComponentType,
+    DesignGraph,
+    Finding,
+    LayoutGraph,
+)
+from backend.periscopex.pcb_net_match import kicad_nets_match
+from backend.periscopex.protocol_catalog import (
+    PhysicalInterface,
+    ProtocolCatalog,
+    ProtocolConstraint,
+    load_catalog,
+    map_protocol_outcome,
+)
+from backend.periscopex.protocol_l0 import _constraint_for, _mandatory
+from backend.periscopex.protocol_recognize import PhysicalBusInstance
+
+PACK_MACROPHASE = "M4"
+SOURCE = "protocol_l2"
+LEVEL = "L2"
+
+L2_CHECKS = frozenset({
+    "differential_impedance",
+    "impedance",
+    "impedance_if_required",
+    "termination",
+    "cc_termination",
+    "voltage",
+    "levels",
+    "rise_time",
+    "fall_time",
+    "return_path",
+    "phy_requirements",
+    "magnetics",
+    "timing",
+    "ac_coupling",
+})
+
+_OHM_UNITS = frozenset({"ohm", "ohms", "ω", "Ω", ""})
+_VOLT_UNITS = frozenset({"v", "volt", "volts"})
+_TIME_UNITS = frozenset({"ps", "ns", "us", "µs", "ms", "s"})
+
+MandatoryClass = Literal["MANDATORY", "RECOMMENDED", "OPTIONAL", "INFORMATIONAL"]
+L2Result = Literal[
+    "PASS", "FAIL", "WARNING", "UNKNOWN", "NOT_APPLICABLE",
+    "VENDOR_DEPENDENT", "CONTROLLER_DEPENDENT", "PHY_DEPENDENT", "MISSING_SOURCE",
+]
+
+
+class L2CheckResult(BaseModel):
+    check: str
+    level: Literal["L2"] = "L2"
+    result: L2Result
+    mandatory: MandatoryClass
+    nets: list[str] = Field(default_factory=list)
+    measured_ohm: float | None = None
+    limit_ohm: float | None = None
+    limit_ohm_min: float | None = None
+    limit_ohm_max: float | None = None
+    margin_ohm: float | None = None
+    value_kind: str = ""
+    notes: str = ""
+    finding_class: str = ""
+    status: str = ""
+
+
+def _pack(
+    check: str,
+    result: str,
+    mandatory: MandatoryClass,
+    *,
+    nets: list[str] | None = None,
+    measured_ohm: float | None = None,
+    limit_ohm: float | None = None,
+    limit_ohm_min: float | None = None,
+    limit_ohm_max: float | None = None,
+    value_kind: str = "",
+    notes: str = "",
+) -> L2CheckResult:
+    if result == "FAIL" and mandatory != "MANDATORY":
+        result = "WARNING"
+    mapped = result
+    if result in {"CONTROLLER_DEPENDENT", "PHY_DEPENDENT"}:
+        mapped = "VENDOR_DEPENDENT"
+    cls, status, _ev = map_protocol_outcome(mapped, mandatory)  # type: ignore[arg-type]
+    margin = None
+    hi = limit_ohm_max if limit_ohm_max is not None else limit_ohm
+    if measured_ohm is not None and hi is not None:
+        margin = hi - measured_ohm
+    return L2CheckResult(
+        check=check,
+        result=result,  # type: ignore[arg-type]
+        mandatory=mandatory,
+        nets=nets or [],
+        measured_ohm=measured_ohm,
+        limit_ohm=limit_ohm,
+        limit_ohm_min=limit_ohm_min,
+        limit_ohm_max=limit_ohm_max,
+        margin_ohm=margin,
+        value_kind=value_kind,
+        notes=notes,
+        finding_class=cls,
+        status=status,
+    )
+
+
+def _num(v: Any) -> float | None:
+    if v is None or isinstance(v, bool):
+        return None
+    try:
+        return float(v)
+    except (TypeError, ValueError):
+        return None
+
+
+def _z_window_from_rule(rule: dict) -> tuple[float, float] | None:
+    lo = _num(rule.get("z_min_ohm"))
+    hi = _num(rule.get("z_max_ohm"))
+    if lo is not None and hi is not None and hi >= lo:
+        return (lo, hi)
+    nom = _num(rule.get("zdiff_ohm")) or _num(rule.get("z0_ohm"))
+    tol = _num(rule.get("tolerance_pct"))
+    if nom is not None and tol is not None and tol > 0:
+        return (nom * (1 - tol / 100.0), nom * (1 + tol / 100.0))
+    if nom is not None:
+        return (nom, nom)
+    return None
+
+
+def intersect_windows(windows: list[tuple[float, float]]) -> tuple[float, float] | None:
+    """Silicon cross: max of mins × min of maxes (PHY subset)."""
+    if not windows:
+        return None
+    lo = max(w[0] for w in windows)
+    hi = min(w[1] for w in windows)
+    if lo > hi:
+        return None
+    return (lo, hi)
+
+
+def electrical_verdict(
+    constraint: ProtocolConstraint | None,
+    measured: float | None,
+    window: tuple[float, float] | None,
+) -> str:
+    """PASS/FAIL only with a cited NUMERIC ohm/volt or a datasheet window."""
+    if window is not None:
+        if measured is None:
+            return "UNKNOWN"
+        if window[0] <= measured <= window[1]:
+            return "PASS"
+        return "FAIL"
+    if constraint is None:
+        return "UNKNOWN"
+    kind = constraint.value_kind
+    if kind == "NUMERIC" and constraint.value is not None:
+        unit = (constraint.unit or "").strip().lower()
+        if unit in _TIME_UNITS:
+            return "UNKNOWN"
+        if measured is None:
+            return "UNKNOWN"
+        if unit in _OHM_UNITS:
+            return "PASS" if abs(measured - constraint.value) < 1e-6 else "FAIL"
+        return "PASS" if measured <= constraint.value else "FAIL"
+    if kind in {
+        "UNKNOWN", "CONTROLLER_DEPENDENT", "PHY_DEPENDENT",
+        "VENDOR_DEPENDENT", "MISSING_SOURCE", "NOT_APPLICABLE",
+    }:
+        return kind
+    return "UNKNOWN"
+
+
+def _instance_nets(inst: PhysicalBusInstance) -> list[str]:
+    names: list[str] = []
+    for g in inst.groups:
+        names.extend(g.nets)
+    names.extend(inst.nets)
+    seen: set[str] = set()
+    out: list[str] = []
+    for n in names:
+        if n not in seen:
+            seen.add(n)
+            out.append(n)
+    return out
+
+
+def _z_rows(impedance_nets: list[dict] | dict | None) -> list[dict]:
+    raw: Any = impedance_nets
+    if isinstance(impedance_nets, dict):
+        raw = list(impedance_nets.get("nets") or [])
+    return [r for r in (raw or []) if isinstance(r, dict) and not r.get("error")]
+
+
+def _row_for(rows: list[dict], net: str) -> dict | None:
+    for row in rows:
+        name = str(row.get("net_name") or row.get("name") or "")
+        if name and kicad_nets_match(name, net):
+            return row
+    return None
+
+
+def _z_from_row(row: dict | None) -> float | None:
+    if not row:
+        return None
+    for k in ("zdiff_ohm", "zdiff_avg_ohms", "z0_avg_ohms", "z0_ohm", "mean_z0", "z0"):
+        v = _num(row.get(k))
+        if v is not None:
+            return v
+    return None
+
+
+def measured_z_ohm(nets: list[str], impedance_nets: list[dict] | dict | None) -> float | None:
+    rows = _z_rows(impedance_nets)
+    vals = [_z_from_row(_row_for(rows, n)) for n in nets]
+    have = [v for v in vals if v is not None]
+    if not have:
+        return None
+    return sum(have) / len(have)
+
+
+def _phy_z_windows(
+    graph: DesignGraph,
+    inst: PhysicalBusInstance,
+    constraints_map: dict[str, ComponentConstraints] | None,
+) -> list[tuple[float, float]]:
+    if not constraints_map:
+        return []
+    refs = [r for r in [inst.host_ref, *inst.peer_refs] if r]
+    inst_nets = set(_instance_nets(inst))
+    for ref, comp in graph.components.items():
+        if ref in refs:
+            continue
+        pins = set(comp.pins.values())
+        if pins & inst_nets:
+            refs.append(ref)
+    windows: list[tuple[float, float]] = []
+    seen: set[tuple[float, float]] = set()
+    for ref in refs:
+        comp = graph.components.get(ref)
+        if comp is None or comp.component_type != ComponentType.IC:
+            continue
+        cons = match_constraints(comp.mpn or comp.value, constraints_map)
+        if cons is None:
+            continue
+        for rule in cons.layout_rules or []:
+            kind = str(rule.get("kind") or "").lower()
+            param = str(rule.get("parameter") or "").lower()
+            if kind not in {"impedance", "zdiff", "z0", "si"} and param not in {
+                "impedance", "zdiff", "z0",
+            }:
+                continue
+            w = _z_window_from_rule(rule)
+            if w and w not in seen:
+                seen.add(w)
+                windows.append(w)
+    return windows
+
+
+def _pack_ohm_window(cons: ProtocolConstraint | None) -> tuple[float, float] | None:
+    if cons is None or cons.value_kind != "NUMERIC" or cons.value is None:
+        return None
+    unit = (cons.unit or "").strip().lower()
+    if unit in _TIME_UNITS or unit in _VOLT_UNITS:
+        return None
+    if unit in _OHM_UNITS or unit in {"", "ohm"}:
+        return (cons.value, cons.value)
+    return None
+
+
+def _skip_z(check: str, mand: MandatoryClass, inst: PhysicalBusInstance, kind: str) -> L2CheckResult:
+    return _pack(
+        check, "UNKNOWN" if kind not in {
+            "MISSING_SOURCE", "PHY_DEPENDENT", "CONTROLLER_DEPENDENT",
+            "VENDOR_DEPENDENT", "NOT_APPLICABLE",
+        } else kind,
+        mand,
+        value_kind=kind,
+        notes=(
+            f"Interfaccia {inst.physical_interface_id} non certificata a L2 "
+            f"per mancanza di Z (datasheet/stackup/fab/cited pack). "
+            f"Not USB/IEC folklore. L0/L1 are not electrical certification."
+        ),
+    )
+
+
+def certify_instance_l2(
+    graph: DesignGraph,
+    inst: PhysicalBusInstance,
+    iface: PhysicalInterface,
+    *,
+    layout: LayoutGraph | None = None,
+    constraints_map: dict[str, ComponentConstraints] | None = None,
+    impedance_nets: list[dict] | dict | None = None,
+) -> list[L2CheckResult]:
+    if inst.pcb_relevant == "NO" or iface.pcb_relevant == "NO":
+        return [_pack(
+            "pcb_routing", "NOT_APPLICABLE", "INFORMATIONAL",
+            notes="Internal interconnect — L2 electrical N/A, not FAIL. L0/L1 are not electrical.",
+        )]
+    checks = [c for c in iface.required_checks if c in L2_CHECKS]
+    if not checks:
+        return []
+    return [
+        _run_l2_check(
+            graph, inst, iface, c,
+            layout=layout,
+            constraints_map=constraints_map,
+            impedance_nets=impedance_nets,
+        )
+        for c in checks
+    ]
+
+
+def _run_l2_check(
+    graph: DesignGraph,
+    inst: PhysicalBusInstance,
+    iface: PhysicalInterface,
+    check: str,
+    *,
+    layout: LayoutGraph | None,
+    constraints_map: dict[str, ComponentConstraints] | None,
+    impedance_nets: list[dict] | dict | None,
+) -> L2CheckResult:
+    mand = _mandatory(iface, check)
+    cons = _constraint_for(iface, check)
+    kind = cons.value_kind if cons else "UNKNOWN"
+    nets = _instance_nets(inst)
+
+    if check in {
+        "differential_impedance", "impedance", "impedance_if_required",
+    }:
+        return _z_check(
+            check, mand, cons, kind, inst, graph, nets,
+            constraints_map, impedance_nets,
+        )
+
+    if check in {"termination", "cc_termination"}:
+        return _termination_check(check, mand, cons, kind, inst, graph, nets, constraints_map)
+
+    if check in {"voltage", "levels"}:
+        return _levels_check(check, mand, cons, kind, inst, constraints_map, graph)
+
+    if check in {"rise_time", "fall_time", "timing"}:
+        return _pack(
+            check, "UNKNOWN" if kind in {"NUMERIC", "UNKNOWN", ""} else kind, mand,
+            nets=nets, value_kind=kind,
+            notes=(
+                "Length is not delay. Rise/fall/timing UNKNOWN without a cited "
+                "time source (no tpd invented from mm). Not L3."
+            ),
+        )
+
+    if check in {"return_path", "magnetics", "phy_requirements", "ac_coupling"}:
+        verdict = kind if kind not in {"NUMERIC"} else "UNKNOWN"
+        if verdict == "NUMERIC":
+            verdict = "UNKNOWN"
+        return _pack(
+            check, verdict, mand, nets=nets, value_kind=kind,
+            notes=(
+                f"{check} not certified without a cited electrical source. "
+                f"Not invented. L0/L1 are not electrical certification."
+            ),
+        )
+    return _pack(check, "UNKNOWN", mand, value_kind=kind, notes="Not an L2 electrical check.")
+
+
+def _z_check(
+    check: str,
+    mand: MandatoryClass,
+    cons: ProtocolConstraint | None,
+    kind: str,
+    inst: PhysicalBusInstance,
+    graph: DesignGraph,
+    nets: list[str],
+    constraints_map: dict[str, ComponentConstraints] | None,
+    impedance_nets: list[dict] | dict | None,
+) -> L2CheckResult:
+    phy = _phy_z_windows(graph, inst, constraints_map)
+    pack_w = _pack_ohm_window(cons)
+    windows: list[tuple[float, float]] = []
+    if pack_w:
+        windows.append(pack_w)
+    windows.extend(phy)
+    window = intersect_windows(windows) if windows else None
+    measured = measured_z_ohm(nets, impedance_nets)
+    if window is None:
+        # no cited pack number and no datasheet PHY window → never invent 90 Ω
+        if measured is None:
+            return _skip_z(check, mand, inst, kind)
+        return _pack(
+            check,
+            kind if kind in {
+                "MISSING_SOURCE", "PHY_DEPENDENT", "CONTROLLER_DEPENDENT",
+                "VENDOR_DEPENDENT", "UNKNOWN",
+            } else "UNKNOWN",
+            mand,
+            nets=nets, measured_ohm=measured, value_kind=kind,
+            notes=(
+                f"Interfaccia {inst.physical_interface_id} non certificata a L2 "
+                f"per mancanza di Z target (cited pack or PHY datasheet). "
+                f"Measured stackup/fab Z is not compared to invented USB/IEC ohms. "
+                f"L0/L1 are not electrical certification."
+            ),
+        )
+    if measured is None:
+        return _skip_z(check, mand, inst, kind)
+    verdict = electrical_verdict(cons, measured, window)
+    source_note = (
+        "PHY datasheet subset × cited pack"
+        if pack_w and phy
+        else ("cited pack" if pack_w else "PHY datasheet subset")
+    )
+    return _pack(
+        check, verdict, mand, nets=nets, measured_ohm=measured,
+        limit_ohm=window[1],
+        limit_ohm_min=window[0],
+        limit_ohm_max=window[1],
+        value_kind=kind if not pack_w else "NUMERIC",
+        notes=(
+            f"L2 Z vs {source_note} {window[0]:g}–{window[1]:g} Ω. "
+            f"Not folklore. Length is not delay. Not L3."
+        ),
+    )
+
+
+def _termination_check(
+    check: str,
+    mand: MandatoryClass,
+    cons: ProtocolConstraint | None,
+    kind: str,
+    inst: PhysicalBusInstance,
+    graph: DesignGraph,
+    nets: list[str],
+    constraints_map: dict[str, ComponentConstraints] | None,
+) -> L2CheckResult:
+    spec_ohm: float | None = None
+    if cons and cons.value_kind == "NUMERIC" and cons.value is not None:
+        unit = (cons.unit or "").strip().lower()
+        if unit in _OHM_UNITS:
+            spec_ohm = cons.value
+    if spec_ohm is None and constraints_map:
+        for ref in [inst.host_ref, *inst.peer_refs]:
+            comp = graph.components.get(ref)
+            if not comp:
+                continue
+            ds = match_constraints(comp.mpn or comp.value, constraints_map)
+            if not ds:
+                continue
+            for rule in ds.layout_rules or []:
+                if str(rule.get("kind") or "") in {"series_resistor", "termination"}:
+                    spec_ohm = _num(rule.get("value_ohms")) or spec_ohm
+    if spec_ohm is None:
+        verdict = kind if kind in {
+            "MISSING_SOURCE", "PHY_DEPENDENT", "CONTROLLER_DEPENDENT",
+            "VENDOR_DEPENDENT", "UNKNOWN", "NOT_APPLICABLE",
+        } else "UNKNOWN"
+        return _pack(
+            check, verdict, mand, nets=nets, value_kind=kind,
+            notes=(
+                f"Interfaccia {inst.physical_interface_id} non certificata a L2 "
+                f"per mancanza di termination cite. No invented Rd/ohm."
+            ),
+        )
+    measured = None
+    netset = set(nets)
+    for comp in graph.components.values():
+        if comp.component_type != ComponentType.RESISTOR:
+            continue
+        if not (set(comp.pins.values()) & netset):
+            continue
+        specs = getattr(comp, "specs", None)
+        ohms = getattr(specs, "value_ohms", None) if specs is not None else None
+        if isinstance(ohms, (int, float)):
+            measured = float(ohms)
+            break
+    if measured is None:
+        return _pack(
+            check, "UNKNOWN", mand, nets=nets, limit_ohm=spec_ohm, value_kind=kind,
+            notes="Termination spec present but resistor value not FACT on the graph.",
+        )
+    verdict = "PASS" if abs(measured - spec_ohm) < 1e-3 else "FAIL"
+    return _pack(
+        check, verdict, mand, nets=nets, measured_ohm=measured, limit_ohm=spec_ohm,
+        value_kind=kind, notes="Termination vs cited/datasheet ohms. Not invented.",
+    )
+
+
+def _levels_check(
+    check: str,
+    mand: MandatoryClass,
+    cons: ProtocolConstraint | None,
+    kind: str,
+    inst: PhysicalBusInstance,
+    constraints_map: dict[str, ComponentConstraints] | None,
+    graph: DesignGraph,
+) -> L2CheckResult:
+    if cons and cons.value_kind == "NUMERIC" and cons.value is not None:
+        unit = (cons.unit or "").strip().lower()
+        if unit in _VOLT_UNITS:
+            return _pack(
+                check, "UNKNOWN", mand, value_kind="NUMERIC",
+                notes="Voltage NUMERIC in pack but PCB rail FACT not supplied — not invented 3.3 V.",
+            )
+    if constraints_map:
+        for ref in [inst.host_ref, *inst.peer_refs]:
+            comp = graph.components.get(ref)
+            if not comp:
+                continue
+            ds = match_constraints(comp.mpn or comp.value, constraints_map)
+            if ds and ds.absolute_maximum_ratings:
+                return _pack(
+                    check, "UNKNOWN", mand, value_kind=kind,
+                    notes=(
+                        "Silicon abs-max present; L2 levels need a cited operating "
+                        "window vs measured rail — not assumed. Not L3."
+                    ),
+                )
+    verdict = kind if kind in {
+        "MISSING_SOURCE", "PHY_DEPENDENT", "CONTROLLER_DEPENDENT",
+        "VENDOR_DEPENDENT", "UNKNOWN", "NOT_APPLICABLE",
+    } else "UNKNOWN"
+    return _pack(
+        check, verdict, mand, value_kind=kind,
+        notes="Levels/voltage UNKNOWN without a cited electrical source. Not invented.",
+    )
+
+
+def l2_findings(inst: PhysicalBusInstance, results: list[L2CheckResult]) -> list[Finding]:
+    out: list[Finding] = []
+    designator = inst.host_ref or inst.physical_interface_id
+    for r in results:
+        if r.result == "PASS":
+            continue
+        if r.result == "FAIL" and r.mandatory != "MANDATORY":
+            continue
+        skip_family = r.result in {
+            "UNKNOWN", "VENDOR_DEPENDENT", "CONTROLLER_DEPENDENT",
+            "PHY_DEPENDENT", "MISSING_SOURCE",
+        }
+        fail = r.result == "FAIL" and r.mandatory == "MANDATORY"
+        na = r.result == "NOT_APPLICABLE"
+        if not skip_family and not fail and not na:
+            continue
+        if fail:
+            rule_id = "PE-PRT-L2-002"
+            status = "ERROR"
+            finding = f"L2 electrical {r.check}: {r.notes}"
+        elif skip_family:
+            rule_id = "PE-PRT-L2-001"
+            status = "WARNING"
+            finding = r.notes or (
+                f"Interfaccia {inst.physical_interface_id} non certificata a L2 "
+                f"per {r.check} ({r.result})."
+            )
+        else:
+            rule_id = "PE-PRT-L0-002"
+            status = "INFO"
+            finding = r.notes
+        f = Finding(
+            designator=designator,
+            mpn="",
+            aspect="protocol_l2",
+            finding=finding,
+            why=r.notes,
+            status=status,
+            source=SOURCE,
+            net=r.nets[0] if r.nets else None,
+            rule_id=rule_id,
+            facts=finding,
+            requirement="L2 Z/termination/levels only from datasheet/stackup/fab/cited pack.",
+            inference="L2 is electrical. L0/L1 are not. Length is not delay. Not L3.",
+            provenance="MANDATORY" if fail else "TYPICAL",
+            finding_class="RULE" if fail else ("REVIEW" if skip_family else "INFO"),
+            evidence_status="INSUFFICIENT" if skip_family else "SUFFICIENT",
+        )
+        out.append(complete_finding(f))
+    return out
+
+
+def certify_l2(
+    graph: DesignGraph,
+    instances: list[PhysicalBusInstance],
+    catalog: ProtocolCatalog | None = None,
+    *,
+    layout: LayoutGraph | None = None,
+    constraints_map: dict[str, ComponentConstraints] | None = None,
+    impedance_nets: list[dict] | dict | None = None,
+) -> tuple[dict[str, list[L2CheckResult]], list[Finding]]:
+    cat = catalog or load_catalog()
+    ifaces = {p.id: p for p in cat.physical_interfaces}
+    by_id: dict[str, list[L2CheckResult]] = {}
+    findings: list[Finding] = []
+    for inst in instances:
+        iface = ifaces.get(inst.physical_interface_id)
+        if iface is None:
+            continue
+        rows = certify_instance_l2(
+            graph, inst, iface,
+            layout=layout,
+            constraints_map=constraints_map,
+            impedance_nets=impedance_nets,
+        )
+        by_id[inst.instance_id] = rows
+        findings.extend(l2_findings(inst, rows))
+    return by_id, findings
diff --git a/periscope/src/backend/services/pcb_pipeline.py b/periscope/src/backend/services/pcb_pipeline.py
index 33e67c8..5ed77ab 100644
--- a/periscope/src/backend/services/pcb_pipeline.py
+++ b/periscope/src/backend/services/pcb_pipeline.py
@@ -376,7 +376,10 @@ async def run_pcb_pipeline(
                 return
 
             _step(project_id, "write_report", "running")
-            proto_section, proto_findings = protocol_exam(graph, layout=layout)
+            proto_section, proto_findings = protocol_exam(
+                graph, layout=layout,
+                constraints_map=cmap, impedance_nets=zrep,
+            )
             findings.extend(proto_findings)
             assign_pcb_finding_ids(findings)
             annotate_findings_cad(findings, cad_index_from_graph(graph))
diff --git a/periscope/src/frontend/content/changelog.md b/periscope/src/frontend/content/changelog.md
index dca8b3e..fec72a1 100644
--- a/periscope/src/frontend/content/changelog.md
+++ b/periscope/src/frontend/content/changelog.md
@@ -2,6 +2,13 @@
 
 What's new in Periscope.
 
+## 2.68.0 — 2026-09-22 — Protocol certification M4 (L2 electrical)
+
+L2 ELECTRICAL certifier: impedance, termination, voltage/levels, rise/fall when sources exist. Z only from datasheet / stackup / fabricator / **cited pack** — never invented 90 Ω USB. USB-IF/IEEE only if the pack has a cite. Silicon cross is max PCB × PHY subset when datasheet windows exist. Length is not delay. No L3/OpenEMS. L0/L1 are **not** electrical. RECOMMENDED never FAIL. MISSING_SOURCE / UNKNOWN when cite is absent. Visible skip when Z cannot be obtained.
+
+- [New] `protocol_l2.py`; `PE-PRT-L2-001` / `PE-PRT-L2-002`.
+- [New] pytest `tests/pcb/test_protocol_l2_m4.py`.
+
 ## 2.67.0 — 2026-09-22 — Protocol certification M3 (L1 geometric)
 
 L1 GEOMETRIC certifier: length, topology, vias, stubs, layer, grouping. Geometric skew only vs **NUMERIC** millimetre or an explicit **DESIGN LIMIT**. Otherwise UNKNOWN / VENDOR_DEPENDENT / CONTROLLER_DEPENDENT / PHY_DEPENDENT — never invent mm/ps. L1 is **not** electrical. No L2/L3. RECOMMENDED never FAIL. Internal interfaces stay NOT_APPLICABLE. Missing DQ/DQS grouping is a visible skip, not PASS.
diff --git a/periscope/src/frontend/package.json b/periscope/src/frontend/package.json
index 86cdd10..3334837 100644
--- a/periscope/src/frontend/package.json
+++ b/periscope/src/frontend/package.json
@@ -1,6 +1,6 @@
 {
   "name": "periscope-web",
-  "version": "2.67.0",
+  "version": "2.68.0",
   "private": true,
   "scripts": {
     "sync-version": "node scripts/sync-version.mjs",
diff --git a/periscope/src/frontend/src/components/report/protocol-section.tsx b/periscope/src/frontend/src/components/report/protocol-section.tsx
index 5f2529e..f5d6e38 100644
--- a/periscope/src/frontend/src/components/report/protocol-section.tsx
+++ b/periscope/src/frontend/src/components/report/protocol-section.tsx
@@ -13,8 +13,9 @@ export function ProtocolSection({
     <section className="rounded-lg border border-border bg-card p-4 space-y-2">
       <h2 className="text-sm font-semibold">Protocolli</h2>
       <p className="text-xs text-muted-foreground">
-        Logical protocol vs physical interface. L0 structural, L1 geometric
-        (length, vias, layer, grouping). Not electrical; no invented ohms/mm/ps.
+        Logical protocol vs physical interface. L0 structural, L1 geometric,
+        L2 electrical (Z from datasheet/stackup/fab or a cited pack — never
+        invented 90 Ω). L0/L1 are not electrical. Length is not delay.
       </p>
       {instances.length === 0 ? (
         <p className="text-sm">{message}</p>
@@ -59,6 +60,14 @@ export function ProtocolSection({
                       .join("; ")}
                   </p>
                 ) : null}
+                {Array.isArray(row.l2_checks) && row.l2_checks.length > 0 ? (
+                  <p className="text-xs text-muted-foreground">
+                    L2{" "}
+                    {(row.l2_checks as Record<string, unknown>[])
+                      .map((c) => `${String(c.check)}=${String(c.result)}`)
+                      .join("; ")}
+                  </p>
+                ) : null}
               </li>
             );
           })}
diff --git a/periscope/src/frontend/src/lib/layout-finding.ts b/periscope/src/frontend/src/lib/layout-finding.ts
index df73b16..7f89d20 100644
--- a/periscope/src/frontend/src/lib/layout-finding.ts
+++ b/periscope/src/frontend/src/lib/layout-finding.ts
@@ -28,6 +28,7 @@ export function isLayoutFinding(f: {
     f.source === "af_trace_check" ||
     f.source === "protocol_l0" ||
     f.source === "protocol_l1" ||
+    f.source === "protocol_l2" ||
     rid.startsWith("PE-PLC") ||
     rid.startsWith("PE-LAY") ||
     rid.startsWith("PE-SI") ||
diff --git a/tests/pcb/test_protocol_l0_m2.py b/tests/pcb/test_protocol_l0_m2.py
index 48bf825..8c31d26 100644
--- a/tests/pcb/test_protocol_l0_m2.py
+++ b/tests/pcb/test_protocol_l0_m2.py
@@ -129,9 +129,9 @@ def test_axi_internal_l0_not_applicable_not_fail():
     assert all(r.result == "NOT_APPLICABLE" for r in rows)
     assert all(r.result != "FAIL" for r in rows)
     sec, findings = protocol_exam(_axi_graph())
-    assert sec.max_level_reached == "L1"
-    from backend.periscopex.protocol_l1 import PACK_MACROPHASE as L1_MACRO
-    assert sec.macrophase == L1_MACRO
+    assert sec.max_level_reached == "L2"
+    from backend.periscopex.protocol_l2 import PACK_MACROPHASE as L2_MACRO
+    assert sec.macrophase == L2_MACRO
     assert all(f.status != "ERROR" for f in findings)
     assert all("AXI_AWVALID" not in (f.net or "") for f in findings if f.rule_id == "PE-PRT-L0-001")
 
diff --git a/tests/pcb/test_protocol_l1_m3.py b/tests/pcb/test_protocol_l1_m3.py
index 940a59f..e6cdc6b 100644
--- a/tests/pcb/test_protocol_l1_m3.py
+++ b/tests/pcb/test_protocol_l1_m3.py
@@ -165,8 +165,8 @@ def test_axi_internal_l1_not_applicable():
     assert all(r.result == "NOT_APPLICABLE" for r in rows)
     assert all(r.result != "FAIL" for r in rows)
     sec, exam_findings = protocol_exam(_axi_graph(), layout=LayoutGraph())
-    assert sec.max_level_reached == "L1"
-    assert sec.macrophase == "M3"
+    assert sec.max_level_reached == "L2"
+    assert sec.macrophase == "M4"
     assert all(f.status != "ERROR" for f in exam_findings)
     blob = json.dumps([r.model_dump() for r in rows])
     assert "electrical certification" not in blob.lower() or "not electrical" in blob.lower()
@@ -257,7 +257,7 @@ def test_l1_does_not_run_impedance():
 
 def test_protocol_exam_attaches_l1_checks():
     sec, _ = protocol_exam(_usb_connected(), layout=_usb_layout())
-    assert sec.max_level_reached == "L1"
+    assert sec.max_level_reached == "L2"
     assert sec.recognized_instances
     row = sec.recognized_instances[0]
     assert row.get("l1_checks")
diff --git a/tests/pcb/test_protocol_l2_m4.py b/tests/pcb/test_protocol_l2_m4.py
new file mode 100644
index 0000000..d012184
--- /dev/null
+++ b/tests/pcb/test_protocol_l2_m4.py
@@ -0,0 +1,261 @@
+"""M4 L2 ELECTRICAL certifier: Z from cite/datasheet/stackup only; never 90 Ω folklore."""
+
+from __future__ import annotations
+
+import json
+
+from backend.periscopex.models import (
+    Component,
+    ComponentConstraints,
+    ComponentType,
+    DesignGraph,
+    LayoutGraph,
+    Net,
+    NetType,
+    PinConnection,
+)
+from backend.periscopex.protocol_catalog import (
+    ConstraintSource,
+    PhysicalInterface,
+    ProtocolConstraint,
+)
+from backend.periscopex.protocol_l0 import protocol_exam
+from backend.periscopex.protocol_l2 import (
+    _pack,
+    certify_instance_l2,
+    certify_l2,
+    electrical_verdict,
+    intersect_windows,
+)
+from backend.periscopex.protocol_recognize import recognize_physical_buses
+
+
+def _ic(ref: str, pins: dict[str, str], *, mpn: str = "", value: str = "") -> Component:
+    return Component(
+        reference=ref, value=value or mpn, footprint="",
+        component_type=ComponentType.IC, mpn=mpn or None, pins=pins,
+    )
+
+
+def _net(name: str, *pairs: tuple[str, str]) -> Net:
+    return Net(
+        name=name, net_type=NetType.SIGNAL,
+        pins=[PinConnection(component_ref=r, pin_number=p) for r, p in pairs],
+    )
+
+
+def _usb_connected() -> DesignGraph:
+    return DesignGraph(
+        components={
+            "U1": _ic("U1", {"1": "USB_D+", "2": "USB_D-"}, mpn="CH340E"),
+            "J2": Component(
+                reference="J2", value="USB2_TypeA",
+                footprint="USB_A",
+                component_type=ComponentType.CONNECTOR,
+                pins={"2": "USB_D+", "3": "USB_D-"},
+            ),
+        },
+        nets={
+            "USB_D+": _net("USB_D+", ("U1", "1"), ("J2", "2")),
+            "USB_D-": _net("USB_D-", ("U1", "2"), ("J2", "3")),
+        },
+    )
+
+
+def _axi_graph() -> DesignGraph:
+    return DesignGraph(
+        components={
+            "U3": _ic("U3", {"1": "AXI_AWVALID"}, mpn="XC7A100T", value="AXI4 interconnect"),
+        },
+        nets={"AXI_AWVALID": _net("AXI_AWVALID", ("U3", "1"))},
+    )
+
+
+def _ddr_graph() -> DesignGraph:
+    pins = {str(i): f"DDR4_DQ{i}" for i in range(8)}
+    pins.update({"8": "DDR4_DQS0_P", "9": "DDR4_DQS0_N"})
+    u_mem = _ic("U5", pins, mpn="MT41K256M16TW", value="DDR4")
+    u_cpu = _ic("U4", {str(i): pins[str(i)] for i in pins}, mpn="STM32", value="MCU")
+    nets = {n: _net(n, ("U5", p), ("U4", p)) for p, n in pins.items()}
+    return DesignGraph(components={"U5": u_mem, "U4": u_cpu}, nets=nets)
+
+
+def _cons(mpn: str, rules: list[dict]) -> ComponentConstraints:
+    return ComponentConstraints(
+        mpn=mpn, pintable=[], absolute_maximum_ratings=[], rules=[],
+        layout_rules=rules,
+    )
+
+
+def _l2_for(graph: DesignGraph, logical_sub: str, **kwargs):
+    insts = recognize_physical_buses(graph)
+    by, findings = certify_l2(graph, insts, **kwargs)
+    rows = []
+    for inst in insts:
+        if logical_sub in inst.logical_protocol_id:
+            rows.extend(by.get(inst.instance_id, []))
+    return rows, findings, insts
+
+
+def _cite() -> ConstraintSource:
+    return ConstraintSource(document="USB 2.0 spec", organization="USB-IF", section="7.1.1")
+
+
+def test_usb_z_missing_source_never_invents_90():
+    zrep = {"nets": [
+        {"net_name": "USB_D+", "z0_avg_ohms": 45.0},
+        {"net_name": "USB_D-", "z0_avg_ohms": 46.0},
+    ]}
+    rows, findings, _ = _l2_for(_usb_connected(), "usb2", impedance_nets=zrep)
+    z = [r for r in rows if r.check == "differential_impedance"]
+    assert z
+    assert z[0].result in {"MISSING_SOURCE", "UNKNOWN"}
+    assert z[0].result != "PASS"
+    blob = json.dumps(z[0].model_dump())
+    assert "90" not in blob
+    assert any(f.rule_id == "PE-PRT-L2-001" for f in findings)
+    assert any("non certificata a L2" in (f.finding or "") for f in findings)
+
+
+def test_usb_z_skip_when_no_stackup_measurement():
+    rows, findings, _ = _l2_for(_usb_connected(), "usb2")
+    z = [r for r in rows if r.check == "differential_impedance"]
+    assert z
+    assert z[0].result in {"MISSING_SOURCE", "UNKNOWN"}
+    assert z[0].measured_ohm is None
+    assert any("mancanza di Z" in (f.finding or "") for f in findings)
+
+
+def test_cited_pack_z_pass_and_fail():
+    graph = _usb_connected()
+    insts = recognize_physical_buses(graph)
+    usb = [i for i in insts if "usb" in i.logical_protocol_id][0]
+    iface = PhysicalInterface(
+        id="usb2-hs-dpair",
+        logical_protocol_id="usb2-hs",
+        bus_type="SERIAL",
+        physical_layer="SERIAL_DIFFERENTIAL",
+        pcb_relevant="YES",
+        required_checks=["differential_impedance"],
+        constraints=[ProtocolConstraint(
+            id="usb-z",
+            parameter="differential_impedance",
+            value_kind="NUMERIC",
+            mandatory="MANDATORY",
+            source_type="STANDARD",
+            source_class="NORMATIVE",
+            value=90.0,
+            unit="ohm",
+            source=_cite(),
+            limit_kind="STANDARD",
+        )],
+    )
+    zrep = {"nets": [{"net_name": "USB_D+", "zdiff_ohm": 90.0}]}
+    ok = certify_instance_l2(graph, usb, iface, impedance_nets=zrep)
+    assert ok[0].result == "PASS"
+    assert ok[0].measured_ohm == 90.0
+    bad = certify_instance_l2(
+        graph, usb, iface,
+        impedance_nets={"nets": [{"net_name": "USB_D+", "zdiff_ohm": 40.0}]},
+    )
+    assert bad[0].result == "FAIL"
+
+
+def test_silicon_cross_phy_subset():
+    assert intersect_windows([(80.0, 100.0), (85.0, 95.0)]) == (85.0, 95.0)
+    graph = _usb_connected()
+    cmap = {
+        "CH340E": _cons("CH340E", [{
+            "kind": "impedance",
+            "z_min_ohm": 80,
+            "z_max_ohm": 100,
+            "note": "CH340E USB",
+            "source_page": 12,
+        }]),
+    }
+    # second PHY on the same nets
+    extra = _ic("U9", {"1": "USB_D+", "2": "USB_D-"}, mpn="USBPHY1")
+    graph.components["U9"] = extra
+    cmap["USBPHY1"] = _cons("USBPHY1", [{
+        "kind": "zdiff",
+        "z_min_ohm": 85,
+        "z_max_ohm": 95,
+        "note": "PHY subset",
+        "source_page": 3,
+    }])
+    zrep = {"nets": [{"net_name": "USB_D+", "zdiff_ohm": 90.0}]}
+    rows, _, _ = _l2_for(graph, "usb2", constraints_map=cmap, impedance_nets=zrep)
+    z = [r for r in rows if r.check == "differential_impedance"]
+    assert z
+    assert z[0].result == "PASS"
+    assert z[0].limit_ohm_min == 85.0
+    assert z[0].limit_ohm_max == 95.0
+    zrep_lo = {"nets": [{"net_name": "USB_D+", "zdiff_ohm": 70.0}]}
+    rows_lo, findings, _ = _l2_for(
+        graph, "usb2", constraints_map=cmap, impedance_nets=zrep_lo,
+    )
+    zlo = [r for r in rows_lo if r.check == "differential_impedance"]
+    assert zlo[0].result == "FAIL"
+    assert any(f.rule_id == "PE-PRT-L2-002" for f in findings)
+
+
+def test_axi_internal_l2_not_applicable():
+    rows, _, _ = _l2_for(_axi_graph(), "axi4")
+    assert rows
+    assert all(r.result == "NOT_APPLICABLE" for r in rows)
+    sec, findings = protocol_exam(_axi_graph())
+    assert sec.max_level_reached == "L2"
+    assert sec.macrophase == "M4"
+    assert all(f.status != "ERROR" for f in findings)
+    blob = json.dumps([r.model_dump() for r in rows])
+    assert "L0/L1 are not electrical" in blob
+
+
+def test_ddr_impedance_phy_dependent_not_invented_ohm():
+    rows, findings, _ = _l2_for(_ddr_graph(), "ddr4")
+    z = [r for r in rows if r.check == "impedance"]
+    assert z
+    assert z[0].result in {"PHY_DEPENDENT", "UNKNOWN", "VENDOR_DEPENDENT"}
+    assert z[0].result != "PASS"
+    blob = json.dumps(z[0].model_dump())
+    assert "40" not in blob
+    assert "90" not in blob
+    assert any(f.rule_id == "PE-PRT-L2-001" for f in findings)
+
+
+def test_length_is_not_delay_timing_unknown():
+    cons = ProtocolConstraint(
+        id="t",
+        parameter="timing",
+        value_kind="NUMERIC",
+        mandatory="MANDATORY",
+        source_type="STANDARD",
+        source_class="NORMATIVE",
+        value=100.0,
+        unit="ps",
+        source=_cite(),
+    )
+    assert electrical_verdict(cons, 12.0, None) == "UNKNOWN"
+
+
+def test_recommended_never_fail_l2():
+    rec = _pack("return_path", "FAIL", "RECOMMENDED", notes="weak")
+    assert rec.result != "FAIL"
+    assert rec.status != "ERROR"
+
+
+def test_l2_does_not_run_l3_or_geometry():
+    rows, _, _ = _l2_for(_usb_connected(), "usb2")
+    assert not any(r.check in {"insertion_loss", "return_loss", "length", "intra_pair_skew"} for r in rows)
+    blob = json.dumps([r.model_dump() for r in rows])
+    assert "openems" not in blob.lower()
+
+
+def test_protocol_exam_attaches_l2_checks():
+    sec, _ = protocol_exam(_usb_connected())
+    assert sec.max_level_reached == "L2"
+    row = sec.recognized_instances[0]
+    assert row.get("l2_checks")
+    assert all(c.get("level") == "L2" for c in row["l2_checks"])
+    assert row.get("l1_checks") is not None
+    assert row.get("l0_checks") is not None