OBD2 Trouble Code P0357: Cylinder G Ignition Coil Circuit Fault

The P0357 trouble code indicates a fault in the ignition coil circuit for cylinder G. This fault can significantly affect engine performance and requires careful diagnosis to identify the exact cause.

This guide covers what P0357 means, common causes, symptoms, diagnostic steps using an OBD2 scanner, and recommended repairs and prevention tips to avoid recurrence.

What P0357 Code Means

The Engine Control Module (ECM) has detected a fault in the primary or secondary ignition coil circuit for cylinder G. In modern ignition systems, most vehicles equipped with OBD2 diagnostics use a coil-on-plug (COP) system where each cylinder has its own ignition coil mounted directly on the engine.

This configuration offers several advantages:

• Reducing energy losses by eliminating ignition wires
• Individual control of ignition timing for each cylinder
• Precise fault detection for each coil

Parameter Settings and Fault Detection

The diagnostic system continuously monitors the electrical circuits between the ECM and the individual ignition coils. The typical circuit includes:

• Battery voltage supply to the coil
• A control pulse from the ECM to activate the spark
• Feedback circuits to monitor operation

When voltage variations in the ignition coil circuit exceed 10% of the manufacturer’s reference parameters, the system:

• Stores the P0357 trouble code
• Illuminates the check engine light on the dash
• May enter a protection mode to prevent engine damage

Symptoms of P0357 Code

Visible symptoms:

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• Check engine light on
• Engine misfires, more noticeable at idle
• Deficient or interrupted acceleration
• Abnormal engine vibrations
• Increased fuel consumption

Advanced symptoms:

• General loss of engine power
• Rough operation at low RPM
• Possible additional codes related to injectors
• Automatic deactivation of the injector for the affected cylinder (on some systems)

Main Causes of P0357 Code

Faulty Ignition Coil

The most common cause is a failing coil itself due to:

• Normal wear from high mileage
• Overheating of internal components
• Deterioration of primary or secondary windings
• Cracks in the coil housing allowing moisture intrusion

Wiring Issues

Electrical faults are a frequent cause:

• Damaged wires due to engine vibration
• Ground shorts or shorts between wires
• Damage from rodents chewing insulation
• Corrosion of contacts in damp areas

Faulty Connectors

The coil connector may exhibit:

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• Corrosion on metal contacts
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PCM Faults

Although rare, PCM issues can include:

• Faulty internal driver circuits
• Software problems in ignition control
• Damage from voltage spikes

Common Diagnostic Mistakes

Many technicians perform unnecessary general maintenance in an attempt to fix the problem:

• Replacing all spark plugs and coils without proper diagnosis
• Costly overhauls of the ignition system
• Ignoring checks of wiring and connectors

A frequently observed issue is wiring damage caused by small animals building nests in the engine bay, chewing insulation.

P0357 Diagnostic Procedure

Required Tools

For a proper diagnosis you’ll need:

• OBD2 scanner for reading codes
• Digital multimeter with AC and Hz functions
• Oscilloscope (optional but recommended)
• Wrenches needed to remove components

Verification Steps

1. Preliminary Visual Inspection

Check all ignition system wiring and connectors:

• Look for signs of damage, burning, or corrosion
• Ensure proper seating of all connectors
• Inspect coils for visible cracks in the housing

2. Reading and Clearing Codes

Connect the scanner and:

• Record all codes stored in memory
• Note freeze-frame data for context
• Clear the codes and test drive

3. Real-World Testing

To reproduce the fault:

• Drive the vehicle under normal conditions
• For automatic transmissions: with the car in Park, have someone hold the brake and gently accelerate to load the engine
• Observe misfires and whether the code reappears

4. Isolating the Affected Cylinder

• Disconnect ignition coil connectors one by one
• When the engine misfire stops, you have identified the faulty coil
• This confirms the issue is related to that specific coil

5. Electrical Testing of the Coil

Using a multimeter in AC Hz mode:

• Measure the signal from the coil connector with the engine running
• A signal between 5–20 Hz indicates a defective coil
• Absence of signal suggests issues in the control circuit

6. Checking Power and Control

Test the circuit voltage:

• Battery voltage (12.6V–13.8V) should be present on the power pin
• Check continuity of the control circuit to the ECM
• Verify there are no shorts to ground

7. Advanced Testing with Oscilloscope

If you have access to an oscilloscope, you can observe:

• The waveform of the control signal
• The charging and discharging times of the coil
• Presence of interference in the signal

Additional Important Checks

Before finalizing the diagnosis, check:

• Crankshaft and camshaft sensor signals
• Proper operation of the fuel system
• Condition of the spark plugs for the affected cylinder

Repairs and Recommendations

For a faulty coil:

• Replace the coil with an OEM part or a quality equivalent
• Check and replace the corresponding spark plug
• Use the torque specification specified by the manufacturer

For wiring issues:

• Repair or replace damaged sections
• Use proper connectors and insulation material
• Protect wiring from future damage

For corroded connectors:

• Clean contacts with electrical contact spray
• Apply dielectric grease for protection
• Replace severely damaged connectors

Preventing Future Issues

To avoid recurrence:

• Perform regular ignition system maintenance
• Replace coils in the manufacturer’s recommended sets
• Protect wiring from rodents with specialized solutions
• Periodically monitor error codes with an OBD2 scanner

The P0357 code requires a methodical approach to accurately identify the cause. A careful diagnosis can save time and costs, avoiding unnecessary component replacements. If diagnosis exceeds your available knowledge, consult a professional automotive technician to prevent further damage to the ignition system.