Comprehensive diagnostic guide for OBD-II code P0362 Ignition Coil L Secondary Circuit Low

Context and code definition (based on verified sources)

• Code identification: P0362 corresponds to the ignition coil L secondary circuit being low. In the Open Source (MIT) definition, this is stated as "Mau funcionamento do primário/secundário da bobina de ignição L" (Ignition coil L primary/secondary malfunction). Translation: Ignition coil L secondary circuit low. Source: Open Source code definition.
• Where this fits in OBD-II: P0362 is a Powertrain Code (a DTC under the broader OBD-II powertrain category). This aligns with the general structure described for OBD-II powertrain codes.

What This Code Means

• The engine control module (ECM/PCM) detected abnormally low voltage or insufficient energy in the secondary winding of ignition coil L when the coil is commanded to fire. This can result in weak or no spark for the cylinder served by coil L, potentially causing a misfire or rough running.
• Important caveat: The lettered coil (coil L) is engine specific. The actual physical coil corresponding to "L" varies by engine. Always consult the vehicle's service information to identify which coil is labeled L on that engine.

Symptoms

• MIL (Check Engine Light) illuminated or flashing in some vehicles
• Misfire indications for the cylinder associated with coil L (may see P030x if misfire codes accompany P0362)
• Rough idle or rough running, especially at idle or under load
• Occasional stalling or hesitation under acceleration
• Degraded engine performance or reduced power (when the coil cannot deliver adequate spark)
• Possible fuel trim adjustments as the ECM attempts to compensate for misfire

Probable Causes

Note: The available sources do not provide NHTSA complaint data for P0362. The following likelihood estimates are informed by typical field diagnostic patterns for ignition coil secondary circuit faults and are presented as realistic probabilities a technician might encounter.

• Faulty ignition coil L (or its internal secondary/driver) - 40% to 60%
  • The coil itself may have degraded insulation, weakened secondary windings, or internal faults reducing secondary voltage.
• Wiring harness or connector to coil L (including coil pack/coil-on-plug harness) - 15% to 30%
  • Damaged, corroded, or loose connectors, broken or high-resistance wiring, or grounding issues can yield a low secondary indication.
• Spark plug, boot, or cylinder-related issues in the same circuit (for cylinder served by coil L) - 5% to 15%
  • A fouled, worn, or misfiring spark plug or a damaged boot/boot-to- coil connection can manifest as weak spark and trigger the coil's secondary fault.
• PCM/drive signal or control circuit fault (ECU/coil driver) - 5% to 10%
  • If the ECM/PCM has an intermittent drive fault or a fault in the high-voltage control path, the coil's secondary circuit may read low.
• Other causes (oil in the coil, water ingress, misrouting of ignition wires, etc.) - 0% to 5%
  • Less common but possible in certain environments or installation conditions.
    Tip: Because P0362 is a secondary circuit fault, engine performance issues tied to coil L are often accompanied by other misfire indicators (P030x codes). If multiple codes appear, follow a systematic approach to isolate the root cause.

What to inspect and test (practical diagnostic plan)

1) Safety and prep

• Ensure the vehicle is on a level surface, in gear/park with parking brake engaged, and the ignition is off before disconnecting any connectors.
• Disconnect the battery if needed to safely inspect wiring and coil connectors; remove the sensor/coil cover carefully.
• Use insulated tools and avoid touching high-voltage conductors. Be aware of stored ignition coil energy even after battery disconnect.

2) Confirm the DTC and collect data

• Use an OBD-II scanner to confirm P0362 and review freeze-frame data to identify engine conditions at the time of fault (engine RPM, load, misfire counters, fuel trim).
• Note any related codes (P030x misfires, P035x ignition coil faults, P0300 random misfire, etc.) that often accompany ignition coil issues.

3) Visual inspection

• Inspect ignition coil L and its harness for obvious damage, oil intrusion, cracks, or signs of overheating.
• Check connectors for corrosion, bent pins, signs of water intrusion, or loose/poorly seated connections.
• Inspect the spark plug for the cylinder served by coil L: fouling, oil fouling, wear, or improper gap.

4) Power and ground verification

• With ignition on but engine off, verify that the coil L primary circuit receives proper battery voltage when commanded (refer to vehicle service data for expected voltage and ground reference).
• Check for a solid ground at the coil L ground circuit. Look for high resistance or intermittent ground faults that could cause weak secondary output.

5) Coil primary and secondary resistance testing (if service data provides spec)

• Measure coil L primary resistance with a digital multimeter (DMM) and compare to the vehicle's specification.
• Measure coil L secondary resistance (roughly across the secondary winding or from the secondary terminal to the correct reference) and compare to manufacturer spec.
• If resistance values are out of spec, replace the ignition coil L (or the entire coil pack/coil-on-plug assembly, depending on design).

6) Spark plug and boot assessment

• Inspect the spark plug and boot connected to cylinder served by coil L for wear, damage, cracks, oil contamination, or compression loss contributing to weak spark.
• Replace spark plug if it is worn or contaminated; ensure correct heat range and gap.

7) Functional testing and swap-test (coil early identification)

• If the engine uses multiple ignition coils, perform a swap test: exchange coil L with another coil position (e.g., coil L with coil M). After swap, recheck the code to see if P0362 moves with the coil (indicating a coil problem) or stays on the same cylinder (indicating a wiring/PCM issue).
• If available, perform a coil-on-plug diagnostic test with a scope or spark tester to observe the actual secondary waveform and ignition energy when coil L is commanded to fire.

8) Wiring and harness checks

• Check all wiring between PCM and coil L for continuity and expected resistance. Look for high resistance, opens, or shorts to ground/other circuits.
• Confirm that any shielded or high-voltage wires are routed properly and not damaged by heat or abrasion.
• Inspect for oil leaks or coolant leaks near coil L that could contaminate the coil or connectors.

9) ECM/PCM considerations

• If coil L tests within spec and wiring is ok, consider the possibility of a PCM output problem. This is rarer but should be considered if no other fault can be found.
• Reprogramming or updating the PCM software may be warranted if the fault code reappears after all hardware checks.

10) Additional checks and cross-correlation

• Look for related codes (P030x, P035x) that confirm misfire or ignition control issues in the same bank/cylinder region.
• Verify ignition timing and any engine mechanical issues that could mask or amplify the coil fault.

Recommended actions based on findings

• Identified faulty coil L or its internal secondary/driver: Replace the ignition coil L (or entire coil pack/coil-on-plug assembly, per engine design). Re-test and clear DTCs; run a road test and re-scan to confirm resolution.
• Faulty wiring/connector to coil L: Repair/replace wiring or connectors; reseat/repair connectors; re-test and re-scan.
• Faulty spark plug or boot on cylinder served by coil L: Replace spark plug and inspect/replace boot as needed; re-test.
• PCM/coil driver fault suspected: Consult service information for possible PCM diagnostics or software update; consider replacement if proven faulty after hardware checks.
• After repairs: Clear the DTCs, perform a drive cycle, and verify that P0362 does not return. Confirm that misfire symptoms are resolved and that related codes (P030x) are cleared or re-evaluated.

Tests and data collection to document

• DTC presence and freeze-frame data (RPM, load, fuel trims)
• Coil L primary and secondary resistance values (vs manufacturer spec)
• Battery voltage and charging system status (provide stable system voltage during tests)
• Wiring continuity/resistance for coil L circuits
• Visual condition of coil L, spark plug, boot, and connectors
• Result of swap-test or functional coil waveform observations (if scope or spark tester is available)

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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