Quick answer: The P0358 code indicates a circuit malfunction in ignition coil ‘H’, which controls cylinder 8. This directly affects your engine’s ignition system, causing noticeable misfires. It is an urgent issue because running a cylinder without proper combustion can allow unburnt fuel to permanently ruin your catalytic converter.
Seeing a Check Engine Light combined with a rough engine can be alarming, but code P0358 points you directly to a problem with cylinder 8. This guide explains what triggers this ignition circuit fault, how to spot the symptoms, and the step-by-step methods to diagnose and fix it.
What Does P0358 Mean?
In modern engines with coil-on-plug ignition systems, the Engine Control Module (ECM) triggers each ignition coil to fire its spark plug at the precise microsecond. Code P0358 means the computer detected an electrical voltage anomaly or complete failure in the primary or secondary control circuit for ignition coil ‘H’-which corresponds to cylinder 8. Whether the circuit is open, shorted to ground, or experiencing excessive resistance, cylinder 8 fails to spark properly, resulting in an active misfire.
Symptoms
- Illuminated Check Engine Light (flashing if the misfire is severe)
- Rough idling and noticeable engine vibration
- Hesitation, jerking, or severe power loss during acceleration
- Engine stalling when coming to a stop
- Reduced fuel economy and a strong smell of unburnt gas from the exhaust
Possible Causes
The most common mistake is replacing the ignition coil immediately without checking electrical connections or spark plugs, which often leads to wasted money on unnecessary parts.
- Loose, corroded, or damaged wiring harness or connector at Cylinder 8
- Defective or failing Cylinder 8 ignition coil
- Worn, fouled, or improperly gapped spark plug in Cylinder 8
- Blown ignition system fuse or faulty engine control relay
- Faulty Engine Control Module (ECM) ignition driver circuit
Check These Yourself Before Visiting a Mechanic
- Visual Wiring Inspection: Pop the hood and inspect the electrical plug on the cylinder 8 coil. Ensure the plastic tab isn’t broken, the connector is pushed in firmly, and no wires are frayed or melted.
- Swap the Coil: Remove the cylinder 8 ignition coil and swap it with an adjacent coil (such as cylinder 7). Clear the codes with an OBD-II scanner. If code P0357 appears after running the engine, the coil itself is broken and needs replacement. If P0358 returns, the problem lies in the wiring or spark plug.
How to Fix It
- Scan the vehicle for additional trouble codes to verify if other cylinders or power circuits are involved.
- Inspect the cylinder 8 wiring harness and electrical connector for corrosion, bent pins, or damaged wire insulation.
- Perform the ignition coil swap test or use a multimeter to check the coil’s primary and secondary resistance.
- Remove and inspect the spark plug in cylinder 8 for wear, oil fouling, or heavy carbon deposits.
- Test for proper 12-volt battery power and ground signals at the ignition coil harness plug using a multimeter.
- Replace damaged components-wiring, spark plug, or ignition coil-based on your test results.
Estimated Repair Costs (2026)
| Job | Parts ($) | Labor ($) |
|---|---|---|
| Spark Plug Replacement | $10 – $25 | $50 – $100 |
| Ignition Coil Replacement | $40 – $120 | $60 – $120 |
| Wiring Harness Repair | $20 – $50 | $100 – $200 |
| ECM Replacement | $400 – $1,000 | $150 – $300 |
Note: These are estimated 2026 repair costs in US dollars. Actual costs vary based on vehicle make, model, engine layout, and local shop labor rates.
Frequently Asked Questions
Can I drive with the P0358 code?
You should avoid driving except to reach a nearby repair facility. Driving with an active misfire sends unburnt fuel into the exhaust, which can rapidly overheat and permanently destroy your catalytic converter, turning a cheap repair into an expensive one.
How do I clear the P0358 code?
After repairing the underlying fault (such as replacing the broken coil or plug), connect an OBD-II scanner to your car’s port under the dash and select ‘Erase/Clear Codes’. Alternatively, the ECM will clear the code on its own after several normal drive cycles without detecting a misfire.
Which cylinder is Coil H on my engine?
Coil ‘H’ refers to cylinder 8 in the engine’s firing order or cylinder layout sequence. Because cylinder numbering arrangements differ between manufacturers (such as Ford, GM, and Chrysler), consult your owner’s manual or engine firing order diagram to locate cylinder 8 accurately.