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P0358 — Ignition Coil H Primary/Secondary Circuit

Severe

Quick answer

P0358 means the engine computer sees an electrical problem in the control circuit of ignition coil H (usually cylinder 8) — the coil isn’t receiving or responding to its firing signal correctly. Unlike a misfire code, this is an electrical-circuit diagnosis: think coil, connector, wiring, or (rarely) the computer itself.

What it means

The ECM fires each ignition coil by switching its primary circuit at exactly the right moment. While doing that, it monitors the circuit’s electrical behavior. P0358 sets when the signal to or from ignition coil H — on nearly every engine that’s the coil for cylinder 8 doesn’t look right — an open circuit, a short, or no response at all.

The practical difference from a misfire code: a misfire code (P0308) says “this cylinder isn’t producing power,” while P0358 says “this coil’s wiring or electronics are faulty.” They often appear together, and when they do, the circuit code is the better starting point because it’s more specific.

Circuit codes are diagnosed with a multimeter and eyes, not by throwing parts: the coil itself is the most common culprit, but a chafed harness or a corroded connector pin causes the exact same code for a tenth of the price.

Common causes

Ordered from most to least likely.

  1. 1.

    Failed ignition coil

    Internal open or short in the coil windings — the most common cause, especially with heat-related, intermittent symptoms.

  2. 2.

    Damaged coil connector

    Corroded, bent, or backed-out pins; a connector that wasn’t fully clicked in after previous plug work is a classic.

  3. 3.

    Chafed or broken wiring

    The harness section to that coil rubbing on a bracket or valve cover edge.

  4. 4.

    Oil in the spark plug well

    A leaking valve cover gasket flooding the coil boot can short the secondary side and damage the coil.

  5. 5.

    Blown fuse or bad ignition relay (multiple-coil cases)

    If several coil circuit codes set at once, check shared power supply first.

  6. 6.

    ECM driver failure

    Rare — only conclude this after the coil, wiring, and connector test good.

How to diagnose it, step by step

Cheapest and most likely checks first.

  1. 1 Scan all codes

    Note whether P0358 appears alone, with a matching misfire code (P0308), or with several coil circuit codes at once — single-coil and multi-coil patterns have different causes.

  2. 2 Inspect the coil and connector

    Unplug the coil, look for bent or corroded pins, green crust, or oil. Check the boot for oil from the plug well — if it’s wet, fix the valve cover gasket too or the new coil will die the same death.

  3. 3 Check power and ground at the connector

    Key on, verify battery voltage on the supply pin and a good ground. No power: trace the fuse/relay and harness. Power present: the coil or its trigger signal is the issue.

  4. 4 Swap the coil with another cylinder

    If the circuit code follows the coil to the new cylinder, the coil is bad — replace it. If the code stays with the original position, the wiring or connector is at fault.

  5. 5 Wiggle-test the harness

    With the engine idling, gently wiggle the harness toward the coil and listen for stumbles — an instant way to find an intermittent chafe.

Parts & tools you may need

  • OBD-II scanner (code reader with freeze frame / live data)
  • Digital multimeter
  • Replacement ignition coil (correct part for your engine)
  • Electrical contact cleaner
  • Dielectric grease
  • Valve cover gasket (if oil is found in the plug well)

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Related codes

Frequently asked questions

Is P0358 the same as a misfire code?
No. P0308 reports the symptom (the cylinder isn’t producing power); P0358 reports an electrical fault in the coil circuit. When both appear, start with the circuit code — it’s more specific.
Can I drive with P0358?
If the coil has actually stopped firing, that cylinder is misfiring and dumping fuel into the exhaust — same catalytic converter risk as any misfire. Drive gently and briefly, or not at all if the light flashes.
Should I replace all the coils at once?
Not necessarily. Unlike spark plugs, coils don’t wear on a fixed schedule. Replace the failed one; consider the rest only if the engine is high-mileage and they’re cheap in a set.
Why did the code come back after a new coil?
Because the circuit — not the coil — was the problem: a chafed wire, corroded pin, or oil refilling the plug well from a leaking valve cover gasket.