P0357 Code: Cylinder 7 Ignition Coil Circuit Fault – Causes & Fixes

The P0357 diagnostic trouble code (DTC) indicates that your vehicle’s engine control module (ECM) has detected a problem with the ignition coil circuit serving cylinder 7. This code is most commonly found in V8 engines, where cylinder numbering varies by manufacturer. The ignition coil is responsible for converting low-voltage battery power into the high-voltage spark needed to ignite the air-fuel mixture in the combustion chamber. When this circuit fails, cylinder 7 cannot fire properly, leading to misfires, poor performance, and increased emissions.

What Does P0357 Mean?

P0357 is a manufacturer-specific code that points to a fault in the ignition coil circuit for cylinder 7. The “0357” breakdown is as follows:

• P = Powertrain system
• 0 = Generic OBD-II code
• 3 = Ignition system
• 57 = Cylinder 7 ignition coil circuit

When the ECM detects abnormal voltage or resistance in the cylinder 7 ignition coil circuit—either too high, too low, or intermittent—it sets this code and illuminates the check engine light. The fault could occur in the coil itself, the wiring harness, connectors, or the PCM’s driver circuit that controls the coil.

Common Symptoms

• Check Engine Light: The primary indicator that P0357 has been triggered
• Engine Misfire: Cylinder 7 fails to fire, causing rough idle and hesitation
• Rough Idle: Noticeable vibration or shaking at stops
• Loss of Power: Reduced acceleration and overall engine performance
• Increased Fuel Consumption: Engine runs rich due to unburned fuel
• Exhaust Smell: Unburned fuel smell from the tailpipe
• Engine Knock or Pinging: Detonation in other cylinders due to imbalanced combustion
• Difficulty Starting: In severe cases, the engine may be hard to start

Possible Causes

Listed from most to least common:

1. Faulty Ignition Coil Pack (Most Common): The ignition coil for cylinder 7 has failed internally or lost its ability to generate sufficient voltage. This is the #1 cause of P0357.
2. Damaged Wiring Harness: Corroded, pinched, or broken wires in the ignition coil circuit can interrupt the signal between the PCM and the coil.
3. Loose or Corroded Connectors: Poor connections at the coil connector or PCM can cause intermittent faults or complete circuit failure.
4. Bad Spark Plug: A fouled or damaged spark plug in cylinder 7 can cause the coil to work harder, triggering a fault code.
5. Engine Control Module (ECM/PCM) Fault: A malfunctioning PCM driver circuit that controls the coil can set this code even if the coil is good.
6. Fuel Injector Issue: A leaking or stuck fuel injector in cylinder 7 can cause misfires that the system interprets as a coil fault.
7. Compression Problem: Low compression in cylinder 7 (due to worn rings, valve issues, or head gasket failure) can cause misfires attributed to ignition failure.
8. Ground Wire Issue: A poor ground connection for the ignition coil circuit can prevent proper operation.

Diagnostic Steps

Follow these steps to diagnose the P0357 code:

Step 1: Scan for Additional Codes

Use an OBD-II scanner to read all stored and pending codes. If you see multiple cylinder misfire codes (P0300, P0301, P0302, etc.), the problem may be more widespread than just cylinder 7’s ignition coil.

Step 2: Inspect the Ignition Coil

Locate the ignition coil for cylinder 7 (consult your vehicle’s service manual for exact location—it’s often mounted directly on the spark plug). Visually inspect for:

• Cracks or damage to the coil housing
• Oil or moisture inside the coil connector
• Burn marks or discoloration
• Loose or corroded connector pins

Step 3: Check Wiring and Connectors

Inspect the wiring harness leading to the cylinder 7 ignition coil:

• Look for pinched, cut, or frayed wires
• Check for corrosion on connector terminals
• Ensure connectors are fully seated and not loose
• Test connector resistance with a multimeter (should be near 0 ohms)

Step 4: Test the Ignition Coil Resistance

Using a multimeter, measure the primary and secondary coil resistance. Consult your vehicle’s service manual for specifications, but typical values are:

• Primary winding: 0.4–2 ohms
• Secondary winding: 5,000–15,000 ohms

If readings are outside these ranges, the coil is faulty and should be replaced.

Step 5: Check Spark Plug

Remove the spark plug from cylinder 7 and inspect it:

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

Step 6: Test for Spark

With the ignition coil connected, use a spark tester or test light to verify that the coil is producing spark. A healthy coil should produce a strong, consistent blue spark.

Step 7: Check Engine Compression

If the coil tests good but the code persists, perform a compression test on cylinder 7. Low compression (below 100 psi) indicates internal engine problems like worn rings or valve issues.

Step 8: Inspect Fuel Injector

Have the fuel injector for cylinder 7 tested for leakage or proper spray pattern. A faulty injector can cause misfires that mimic ignition problems.

Step 9: PCM Testing

If all other components test good, the PCM may be faulty. This requires professional diagnostic equipment and should be performed by a qualified technician.

Repair Cost Estimates

The cost to repair P0357 varies depending on the root cause:

• Ignition Coil Replacement: $150–$400 per coil (parts + labor). This is the most common repair.
• Spark Plug Replacement: $100–$300 for one spark plug and labor
• Wiring Harness Repair/Replacement: $200–$600 depending on extent of damage
• Connector Repair: $50–$200 for cleaning, repair, or replacement
• Fuel Injector Replacement: $300–$900 if the injector is faulty
• PCM Reprogramming/Replacement: $500–$1,500+ (rarely needed)
• Compression Repair (Engine Work): $1,000–$5,000+ if internal engine damage is found

Tip: Start with the ignition coil replacement, as it’s the most common cause and the least expensive fix. If the code returns after coil replacement, proceed to more complex diagnostics.

Can I Still Drive?

Severity: High

While you may be able to drive short distances with P0357, it is not recommended for extended periods. Here’s why:

• Engine Misfire: Cylinder 7 not firing properly puts extra stress on the remaining cylinders and can damage the catalytic converter if unburned fuel ignites inside it.
• Reduced Performance: You’ll experience poor acceleration, rough idle, and reduced fuel economy.
• Emission Violations: The vehicle will fail emissions testing and may be illegal to drive in some jurisdictions.
• Potential Engine Damage: Prolonged driving with a misfire can damage the catalytic converter, requiring a costly replacement ($800–$2,500).
• Safety Concerns: Loss of power during acceleration could be dangerous in traffic or highway driving.

Recommendation: Have the code diagnosed and repaired as soon as possible. Most ignition coil replacements can be completed in under an hour, making this a relatively quick and affordable fix.

Frequently Asked Questions