OBD-II trouble code
P0358: Ignition Coil 'H' Primary/Secondary Circuit
The eighth coil, and the last one a V8 can report. Eight coils bought at the same time and heat-cycled the same number of times do not fail independently — which makes this a question about the set, and about what you buy to replace it.
Quick facts
- System
- Powertrain
- Category
- Ignition
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $55 – $1,100
- DIY difficulty
- Intermediate DIY
What does P0358 mean?
'H' closes the alphabet for a V8. Eight independently driven outputs is exactly what an eight-cylinder engine has, so this is the top of the range for one of the most numerous engine layouts still in service. What makes the eighth coil worth a page of its own is not where it sits — it is what it implies about the other seven.
Coils on a factory engine are a matched cohort. They were manufactured in the same batch, fitted on the same day, and have since experienced the same number of heat cycles under the same underhood conditions. Failure of an electrical component driven by insulation degradation is not a random event spread evenly across time; it clusters. When the first coil in a set of eight goes at 110,000 miles, the honest reading is not that one coil was unlucky. It is that the whole set has reached the part of its life where failures begin, and the remaining seven are drawing from the same pool.
That is the argument for replacing the set, and it is a genuinely strong one on a V8 for a reason that has nothing to do with the coils themselves: the labour. On most pushrod V8s the coils sit on top of the valve covers, exposed, held by two bolts each, and the labour to do all eight is not far off the labour to do one. When the marginal labour is near zero, the only question is parts cost, and the tradeoff becomes a straightforward comparison between one coil now plus the risk of seven more roadside failures, and eight coils now with the matter closed.
Which leads to the thing that actually decides the outcome: what you buy. Eight-coil sets are sold online at prices that are a fraction of what one manufacturer coil costs, and the reason they can be is that the expensive parts of a coil are the ones you cannot see — the quality of the potting compound, the insulation between windings, the sealing of the boot. A cheap set will fire the engine perfectly on the day it is fitted and can start failing within a year or two, at which point you have paid for the job twice and learned nothing. The economics that make set replacement sensible only hold if the set you fit lasts, and a set of quality coils fitted once is very often cheaper over five years than two sets of the cheapest available. If budget forces a choice, one good coil beats eight poor ones.
One caveat on the cohort argument. It applies to age-and-heat failure, which is what you see on an original set at high mileage. It does not apply when the failure had an external cause — oil flooding a plug well from a leaking valve cover, water from a washed engine bay, a connector damaged during other work, or a plug left past its interval. Those are single-cylinder events, the other coils are unaffected, and replacing all eight in response to one of them is spending money on a problem you do not have. Establish which of the two situations you are in before deciding how much to buy.
Common causes
- Age and heat-cycle failure of an original coil in a set that has all reached the same point in its life
- Previously fitted low-quality replacement coil with inadequate internal insulation, failing within a year or two of installation
- Oil in the spark plug well from a leaking valve cover gasket, degrading the boot on one cylinder only
- Spark plug left well past its replacement interval, with a gap wide enough to stress the coil into breakdown
- Corroded or heat-damaged coil connector
- Chafed or heat-damaged section of the ignition harness near an exhaust manifold or heat shield
- Failed coil driver inside the engine control module
- Mixed-brand coil set, where an outlier unit behaves differently from the rest and complicates comparison testing
Symptoms
- Check engine light on, sometimes flashing while the misfire is active
- Misfire on one cylinder with a distinct shake at idle
- Repeat coil failures on different cylinders over a short period, which points at the set rather than at one unit
- Loss of power and hesitation under acceleration
- Rough running that is worst when the engine is cold and improves as it warms
- Increased fuel consumption and unburnt fuel smell from the exhaust
Diagnostic steps
- 1.Establish whether the coils are original and how many miles they have done. An original set at high mileage points at cohort failure; a recently fitted budget set points at part quality.
- 2.Ask whether any coil on this engine has been replaced before, and when. Two coil failures on different cylinders within a year is the clearest possible signal that the set is finished.
- 3.Look for an external cause before assuming age. Oil in the plug well, water in the boot, a damaged connector or a badly overdue spark plug all produce single-cylinder failures that say nothing about the other seven.
- 4.Compare primary resistance across all eight coils. Uniform readings with one clear outlier suggests a single failure; readings that are drifting across the whole set suggests the cohort is going.
- 5.Check the spark plugs. Plugs and coils age together, and a set of worn plugs is both a cause of coil stress and a sign the ignition system as a whole is overdue.
- 6.Swap the suspect coil to another cylinder and confirm the fault follows it, which is cheap on most V8s because the coils are accessible on top of the valve covers.
- 7.If replacing the set, fit coils of consistent and known quality rather than the cheapest available. The labour saving that justifies doing the set is lost entirely if the set has to be done again.
- 8.Replace the spark plugs at the same time as a set replacement. They are inexpensive relative to the job and a worn plug will shorten the life of a new coil.
Repair cost
$55 – $1,100
One coil is typically $55 to $220 in parts with about half an hour of labour on an accessible pushrod V8, so a single-coil repair commonly lands between $110 and $350. A full set of eight quality coils is usually $400 to $1,100 installed, and because the labour to reach all eight is only slightly more than for one, most of that increase is parts. Budget eight-packs sold for $80 to $150 exist and are the most common reason this job gets paid for twice. Add spark plugs at $60 to $250 for the set if they are due.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with ignition coil replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.