OBD codes / P0358
P0358
SeriousIgnition Coil H Primary/Secondary Circuit (Cylinder 8)
One of eight cylinders misfiring may barely register from the driver's seat, which makes P0358 easy to ignore — don't. The unburned fuel from cylinder 8 still overheats the catalytic converter on that bank. Drive lightly and briefly if you must, and treat a flashing check-engine light as a stop-and-repair signal.
What this code means
P0358 is the ECM reporting an open or short in the primary or secondary circuit of ignition Coil H — cylinder 8's coil, which makes this a code for V8 and larger engines. On coil-on-plug systems the computer drives every coil individually through its primary winding and checks the circuit each time it commands a spark, so the code identifies the exact coil circuit at fault. Keep the diagnosis electrical: a worn spark plug weakens the spark but doesn't open the circuit, so the suspects are the coil itself, its connector, the wiring leg feeding it, the fuse supplying the coil bank, and — rarely — the driver transistor inside the ECM. Cylinder 8 is typically the last cylinder on one bank of a V8, though which bank depends on the manufacturer's numbering; on some engines it sits close to the firewall where connectors get disturbed during other work. Expect the matching misfire code P0308 alongside, since the cylinder has lost spark entirely.
Symptoms you might notice
- Cylinder 8 misfire — rough idle with a rhythmic miss
- Noticeable power loss under acceleration or load
- Flashing check-engine light during active misfire
- Raw-fuel smell from the exhaust
- Reduced fuel economy; P0308 usually stored with it
What it costs to fix
Typical range: $60–$450 · about ~0.2–2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Ignition coil (single) | $30–$150 | ~0.2–1 hrs |
| Wiring or connector repair | $5–$50 | ~0.5–2 hrs |
| Spark plugs (while in there) | $20–$100 | ~0.5–1.5 hrs |
On most V8s the coils are exposed on top of the engine, so a confirmed bad coil is a quick, inexpensive swap. Rear-of-bank cylinders like number 8 can be tighter to reach on some trucks and rear-drive sedans with deep engine bays, and intermittent wiring faults add tracing time regardless of layout.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0358 for my exact vehicle →
Frequently asked
Could a fuse cause P0358?
Yes — the ignition coils are fed through a fuse (sometimes a relay), and a blown one kills coil power. Usually that takes out several coils at once and sets multiple codes, so a lone P0358 more often points to coil 8 itself or its connector and wiring. Either way, the fuse box is a 30-second check worth doing first.
My V8 runs almost normally — do I really need to fix P0358?
Yes. A V8 masks one dead cylinder well, but the misfire is still pushing raw fuel into the catalytic converter every second the engine runs, and converters fail by overheating. The fix is typically one cheap coil; the consequence of ignoring it can be an exhaust repair costing many times more.
Should I replace all eight coils?
Only if you want to. If the swap test confirms coil 8 failed and the others behave, one coil is a complete repair. On a high-mileage engine some owners do the full set (and plugs) as preventive maintenance since coils of the same age tend to fail in sequence — that's a convenience decision, not a requirement.
Will P0358 pass or fail an emissions test?
An active check-engine light generally means an automatic fail wherever OBD testing is used. Repair the circuit, clear the code, and drive enough for the readiness monitors to complete before retesting.
Seeing P0358 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0358 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.