P0358 Code: Ignition Coil H Primary/Secondary Circuit
Coil H, for cylinder 8, has an electrical fault. On nearly every V8 it's the hardest coil to reach.
At a glance
Severity: Moderate
- Meaning
- Ignition Coil H Primary/Secondary Circuit
- System
- Ignition & Misfire · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $50–$1,600
- DIY difficulty
- Moderate
P0358 is set when the engine computer fires its eighth coil output and doesn't see the primary current or feedback signal it expects. The code exists on V8 and larger engines, and on almost all of them cylinder 8 sits at the rear, against the firewall. Only the side changes: passenger side on GM and Chrysler V8s, driver side on Ford V8s, where it sits under the cowl beside the brake booster. That position explains most P0358 faults. The rear of the engine gets the least airflow and the most heat soak after shutdown, water from blocked cowl drains finds its way into the rear plug wells, and a connector that is hard to see is easy to leave unlatched after plug work.
Can I keep driving? The truck or car will limp along on seven cylinders, but keep it to short, easy trips. If the check-engine light flashes, stop, because the catalytic converter on that bank is being flooded with fuel.
How to read P0358
- P Powertrain
- 0 Generic (SAE)
- 3 Ignition / misfire
- 58 Specific fault
Symptoms
- Steady miss at idle that you can feel through the floor
- Check-engine light with P0308, flashing under load
- Miss worst on a hot restart after a short stop
- Problem started after heavy rain or a car wash
- Slightly cooler exhaust manifold runner at the rear of one bank
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Coil H has failed, often from years of heat soak at the firewall
- Water in the cylinder 8 plug well from blocked cowl drains, corroding the boot and coil
- Coil H connector not latched after plug work, or its locking tab broken
- Coil H wiring chafed against the firewall or a bracket at the back of the cylinder head
- Worn spark plug demanding more voltage than the coil can deliver
- Feed or ground shared by the coils on cylinder 8's bank has a poor connection
- Coil H driver in the engine computer has failed
Diagnosis step by step
Find cylinder 8 and plan the access
On GM and Chrysler V8s it is the rear passenger-side cylinder. On Ford V8s it is the rear driver-side cylinder, under the cowl next to the brake booster. Expect to remove the air intake duct, and on some Ford trucks part of the cowl or wiper panel, to reach it properly.
Tools: Flashlight, Screwdriver
Confirm cylinder 8 is dead without tearing into it
A scan tool with a cylinder power balance test will show no rpm drop when cylinder 8 is disabled if it is already dead. Without one, measure the exhaust manifold runners with a temperature probe or infrared thermometer a minute or two after a cold start: the runner of a dead cylinder stays noticeably cooler.
Tools: OBD-II scanner, Multimeter
Check the well for water and the cowl drains
Pull coil H and look into the well with a light. Standing water, rust on the plug or a green corroded spring means water is getting in. Clear the cowl drains and check the cowl seal before replacing anything, or the new coil will drown too.
Tools: Flashlight, Gloves
Swap coil H with another coil on the same bank
Swap coil H with coil 6 on GM and Chrysler, or with coil 7 on Ford, since those share the bank. Clear the codes and drive until the engine is fully warm. If the fault follows the coil, replace it. If it stays with cylinder 8, keep working on the wiring.
Tools: Screwdriver, OBD-II scanner
Work the connector and harness at the back of the head
Make sure the connector latch clicks, then with the engine idling flex the coil H harness where it bends around the back of the cylinder head and along the firewall. A stumble while flexing one spot locates a broken wire.
Tools: Flashlight, OBD-II scanner
Replace the plug while you're in there
Because access is the hard part, replace plug 8 at the same time and check its gap. Reinstall the cowl seals and any heat shields you removed so water and heat stay away from the new coil.
Tools: Spark plug socket, Torque wrench
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace coil H (with cowl or intake removal) | Yes | $150–$400 |
| Replace coil H and plug 8 together | Yes | $180–$450 |
| Clear cowl drains and reseal the cowl | Yes | $50–$200 |
| Repair coil H harness at the firewall | No | $120–$350 |
| Replace engine computer (rare) | No | $700–$1,600 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
With P0358 stored and the check-engine light on, the vehicle fails an OBD-II emissions test in states that require one. Light-duty trucks under the weight limit are tested like cars, so fix the coil and let the monitors complete before the appointment.
Frequently asked questions
Why is coil 8 always the hardest to reach?
On almost every V8 cylinder 8 is the last cylinder on its bank, at the firewall. The cowl, the brake booster, the air intake and the heater hoses all crowd around it, which is also why it runs hotter than the front coils.
Can I confirm cylinder 8 is dead without taking things apart?
Yes. A power balance test with a capable scan tool, or comparing exhaust runner temperatures right after a cold start, both show which cylinder is not firing. That saves you pulling the cowl for the wrong cylinder.
Water keeps getting into the cylinder 8 well. Why?
Usually blocked cowl drains, a torn cowl seal or a coil seal that no longer grips the well. Leaves and dirt collect at the base of the windshield and send rainwater straight down onto the rear of the engine.
Does P0358 on its own mean the computer is bad?
Rarely. Coils, water damage and connectors account for most cases. Only when a known-good coil, a clean connector and a verified wire to the computer still give P0358 should the driver in the computer be suspected.