P0358 Code: Cylinder 8 Ignition Coil Circuit Fault

If your vehicle has triggered the P0358 diagnostic trouble code, your engine’s onboard computer has detected a malfunction in the ignition coil circuit responsible for firing cylinder 8. This is a high-severity code that affects engine performance and should be addressed promptly. In this guide, we’ll explain what this code means, what causes it, how to diagnose it, and what you can expect to pay for repairs.

What Does P0358 Mean?

P0358 is a manufacturer-specific diagnostic trouble code that indicates the engine control module (ECM) has detected a fault in the ignition coil circuit for cylinder 8. This code is most commonly found on V8 engines, where cylinder 8 is typically the last cylinder in the firing order.

The ignition coil is responsible for converting low voltage from the battery into the high voltage needed to create a spark at the spark plug. When the ECM detects a problem with this circuit—such as an open circuit, short circuit, or abnormal voltage—it stores the P0358 code and illuminates the check engine light.

The “circuit fault” designation means the problem is electrical in nature, affecting the coil’s ability to function properly. This could involve the coil itself, the wiring harness, connectors, or the ECM’s ability to control the coil.

Common Symptoms

• Check Engine Light: The most obvious symptom; the MIL (malfunction indicator lamp) will be illuminated on your dashboard
• Engine Misfire: Cylinder 8 will fail to fire properly, causing a noticeable rough idle or stumbling sensation
• Loss of Power: Reduced engine performance and acceleration, especially under load
• Rough Idle: The engine may shake or vibrate at a standstill or at low RPMs
• Poor Fuel Economy: Unburned fuel in cylinder 8 reduces overall efficiency
• Difficulty Starting: In severe cases, the engine may be hard to start or fail to start entirely
• Exhaust Smell: Unburned fuel may create a strong fuel smell from the exhaust
• Catalytic Converter Damage Risk: Prolonged misfires can damage the catalytic converter due to unburned fuel entering it

Possible Causes (Ranked by Likelihood)

1. Faulty Ignition Coil Pack (Most Common): The ignition coil for cylinder 8 has failed internally, preventing proper spark generation. This is the most frequent cause of P0358.
2. Damaged Wiring or Connectors: Corroded, burned, or disconnected wiring between the ECM and the coil, or a loose/faulty connector at the coil pack itself.
3. Spark Plug Issues: A worn, fouled, or incorrectly gapped spark plug in cylinder 8 can cause the coil circuit to work harder and trigger a fault code.
4. Engine Control Module (ECM) Problem: A malfunctioning ECM or a corrupted software issue preventing proper coil control (less common).
5. Fuel Injector Malfunction: A faulty fuel injector in cylinder 8 causing a misfire that the ECM interprets as a coil circuit fault.
6. Compression Problem: Low compression in cylinder 8 due to worn piston rings, valve issues, or head gasket failure can cause misfires attributed to coil failure.
7. Ground Connection Issues: Poor ground connections between the coil pack and the engine block or ECM can cause circuit faults.

Diagnostic Steps

Follow these steps to diagnose the P0358 code:

Step 1: Scan for Additional Codes

Use an OBD-II scanner to check for other related codes. Codes like P0300 (random misfire), P0308 (cylinder 8 misfire), or P0200 (fuel injector circuit) may provide additional clues about the root cause.

Step 2: Visual Inspection

Inspect the ignition coil pack for cylinder 8:

• Look for visible damage, cracks, or burn marks on the coil
• Check the connector for corrosion, loose pins, or damage
• Examine the wiring harness for cuts, abrasions, or melting
• Verify all connections are secure and properly seated

Step 3: Check Spark Plug

Remove the spark plug from cylinder 8 and inspect it:

• Look for excessive wear, fouling, or carbon buildup
• Check the gap with a gap tool (should match manufacturer specifications)
• Replace if worn or damaged

Step 4: Test Coil Resistance

Using a multimeter, test the ignition coil’s primary and secondary resistance:

• Disconnect the coil pack from its connector
• Set the multimeter to ohms (resistance) mode
• Measure primary resistance (typically 0.4–2 ohms) and secondary resistance (typically 5,000–15,000 ohms)
• Compare readings to manufacturer specifications; out-of-range values indicate a faulty coil

Step 5: Test Wiring and Connectors

Check the circuit between the ECM and the coil:

• Use a multimeter to test for continuity in the wiring harness
• Check for proper voltage at the coil connector (typically 12V with the key on)
• Test ground connections for proper continuity

Step 6: Check Engine Compression

If the coil and spark plug test normal, perform a compression test on cylinder 8:

• Low compression (below 100 psi) indicates internal engine problems like worn rings or valve issues
• This would explain the misfire even with a functioning coil

Step 7: Scan ECM for Software Issues

If all electrical components test normal, the ECM itself may need reprogramming or replacement. This is rare but possible.

Repair Cost Estimates

The cost to repair a P0358 code varies depending on the underlying cause:

• Ignition Coil Replacement: $150–$400 per coil (most common fix). Labor typically adds $50–$150, depending on coil accessibility.
• Spark Plug Replacement: $20–$100 total for one spark plug, including labor.
• Wiring or Connector Repair: $100–$300 for diagnosis and repair of damaged wiring or connectors.
• ECM Reprogramming: $300–$800 if software corruption is the issue.
• ECM Replacement: $1,000–$2,500 if the module itself has failed (rare).
• Engine Internal Repairs: $1,000+ if compression issues require valve work or piston ring replacement.

Average Total Cost: Most P0358 repairs fall in the $200–$500 range when the ignition coil is the culprit, which is the case in approximately 80% of occurrences.

Can I Still Drive?

Severity: HIGH

While you may be able to drive a vehicle with a P0358 code, it is not recommended for extended periods. Here’s why:

• Engine Misfire: A misfiring cylinder reduces engine efficiency and power output, making acceleration sluggish and potentially unsafe in traffic situations.
• Catalytic Converter Risk: Prolonged misfires send unburned fuel into the exhaust system, which can overheat and damage the catalytic converter. Catalytic converter replacement costs $800–$2,500.
• Fuel Economy: You’ll notice a significant drop in MPG, wasting fuel and money.
• Engine Damage: Continuous misfires can lead to carbon buildup and potential long-term engine damage.
• Emissions Testing: Your vehicle will fail emissions testing with this code active.

Recommendation: Have the code diagnosed and repaired as soon as possible. If you must drive the vehicle, do so carefully and avoid highway speeds or heavy acceleration. Get it serviced within a few days to prevent further damage.

Frequently Asked Questions