P0357 Code – Ignition Coil G Primary/Secondary Circuit Malfunction – Full Diagnosis & Repair Guide (2026)

1‑Minute Quick Check

1. Is the check‑engine light flashing? A flashing light indicates multiple misfires and can damage the catalytic converter.
2. Do you hear a single‑cylinder “pop” at idle? That sound often points to coil G.
3. Can you spot any broken or corroded wires near the coil pack? A visual defect can be identified in under a minute.

If any answer is “yes,” move on to the detailed troubleshooting steps.

What the Driver Will Feel

• Rough idle – the engine shakes or stalls around 600‑800 RPM.
• Loss of power – noticeable hesitation when you press the accelerator, especially under load.
• Engine vibration – a thudding sensation that grows louder as you accelerate.
• Check‑engine light – P0357 stored in the PCM, often accompanied by a generic misfire code (P0300‑P0308).

These symptoms are common on Toyota, Honda, Ford, and Chevrolet models that use distributor‑less ignition systems.

Why P0357 Appears

Wiring Faults

Corroded pins, cracked harnesses, or loose clamps interrupt the voltage that the PCM sends to coil G. The PCM then records an abnormal voltage or resistance.

Coil Degradation

Coils age, especially in high‑temperature bays. A weakened coil cannot generate enough spark, causing a misfire on its cylinder.

PCM Driver Trouble

The PCM contains driver transistors that switch coil voltage on and off. A failed driver can leave coil G without power even when the coil itself is healthy.

Fuse or Power‑Supply Issues

A blown 10 A ignition‑coil fuse or a low‑voltage battery can starve the coil of the energy it needs, prompting the PCM to set P0357.

Tools & Preparation Checklist

Having these tools on hand reduces the chance of returning to the garage for a missed step.

Safety First

• Battery disconnect – Always disconnect the negative battery terminal before removing any coil or connector. This prevents accidental sparks.
• Hot exhaust caution – Wait at least 15 minutes after the engine shuts off; the exhaust can stay above 200 °F and cause burns.
• Jack stands – If you need to lift the vehicle to access the coil pack, use jack stands; never rely on a jack alone.
• Fuel system awareness – Do not spray cleaning fluid near open fuel injectors or the fuel rail. A spark near fuel can ignite vapors.

Following these precautions protects you and the vehicle.

Understanding the Ignition‑Coil G Circuit

The primary circuit carries battery voltage to the coil’s primary winding. The PCM switches this voltage on and off according to engine speed and load. The secondary circuit transfers the high‑voltage spark to the spark plug. Any break in either circuit—whether a high‑resistance splice, a shorted wire, or a failed coil—will cause the PCM to log P0357.

Step‑by‑Step Diagnosis & Repair

1. Quick Visual Scan

Shine a flashlight on the coil‑G harness. Look for burnt connectors, frayed wires, or loose clamps. If you find damage, replace the affected wire or connector before proceeding.

2. Fuse & Power Check

Locate the “IGN COIL” fuse (usually 10 A). Pull it and inspect the filament. Replace if broken. With the fuse re‑installed, set the multimeter to DC volts, attach the probes to the coil‑G connector, and compare the reading to the battery voltage (≈12.6 V). A reading below 11 V suggests a power‑supply problem.

3. Live Data Review

Connect an OBD‑II scanner, select “Live Data,” and find PID 44 (Ignition Coil G Voltage). At idle (≈1500 RPM), the voltage should be steady and close to battery voltage. Large spikes or a constant 0 V reading indicates a wiring fault or coil failure.

4. Primary Resistance Test

Safety: Disconnect the negative battery terminal first. Remove the coil‑G connector, then place the multimeter leads on the primary terminals (pins 1 & 2). Most manufacturers specify 0.5‑2 Ω. A reading outside this range means the coil is shorted or open and must be replaced.

5. Swap‑Coil Confirmation

Swap coil G with another cylinder’s coil (e.g., coil A). Re‑install, clear the code, and take a short test drive. If the misfire follows the coil, the coil is defective. If the misfire stays on cylinder G, the wiring or PCM is at fault.

6. PCM Connector Inspection

Locate the PCM’s coil‑G connector—often tucked under the intake manifold. Remove the connector, spray a small amount of contact cleaner on the pins, and reseat it firmly. Corrosion can cause intermittent voltage loss.

7. Clear & Verify

Use the scanner’s “Clear DTC” function. Drive the vehicle for at least 15 minutes, including a highway pass (≥45 mph) to complete a full drive cycle. Re‑scan; if P0357 does not return, the repair was successful.

Cost Breakdown

Emissions impact: Because the code monitors a misfire that can increase unburned hydrocarbons, any vehicle with an active P0357 will fail a state emissions inspection until the fault is cleared.

Model‑Specific Guidance

Toyota (2.5 L 4‑cyl, 2020‑2023 Camry)

Moisture often infiltrates the coil pack. Replace the coil ($45) and apply dielectric grease to the connectors. Labor at an independent shop averages $80.

Honda (1.5 L VTEC, 2019‑2022 Civic)

Cracked harnesses near the valve cover are common. A wiring‑repair kit ($25) plus $90 labor usually resolves the issue.

Ford (5.4 L V8, 2015‑2018 F‑150)

Heavy towing stresses the PCM driver. After coil replacement ($70), many owners need a PCM driver repair ($250 part) at a dealership.

Chevrolet (6.2 L V8, 2016‑2020 Silverado)

Heat‑related solder joint cracks in the coil are typical. Upgrading the heat shield ($30) and installing a new coil ($60) with $100 labor fixes the problem.

Preventive Maintenance Tips

• Inspect coils annually for cracks, carbon buildup, or discoloration.
• Apply dielectric grease to coil connectors after each service to keep moisture out.
• Test battery voltage regularly; a weak battery can cause low‑voltage coil operation.
• Replace spark‑plug wires (if equipped) every 60 000 mi to maintain a solid secondary circuit.
• Keep the engine bay clean; oil and debris can accelerate corrosion on wiring.

Can You Still Drive With P0357?

Yes, short trips are possible, but expect a rough idle, reduced acceleration, and a high likelihood of failing an emissions test. Avoid prolonged high‑load driving (towing, steep hills) until the coil‑G circuit is repaired.

Frequently Asked Questions

Q: Does P0357 always mean a bad coil? A: No. While a faulty coil is common, wiring faults, PCM driver issues, or a blown fuse can also trigger the code.

Q: Will clearing the code without fixing anything make the problem disappear? A: The scanner can erase the code temporarily, but the PCM will set it again within a few drive cycles if the underlying fault remains.

Q: Is a PCM replacement ever necessary? A: Only when the driver transistor for coil G is confirmed dead after all other tests. This is rare and usually performed by a dealer.

Q: How does a misfire affect fuel economy? A: Unburned fuel from a misfire can reduce mileage by 5‑10 % and increase exhaust emissions.

When to Seek Professional Help

• The coil passes resistance tests, live data looks normal, and the code still returns after swapping coils.
• You detect damage to the PCM connector that cannot be cleaned or reseated.
• The vehicle’s warranty is still active and you prefer dealer service for PCM work.

Professional technicians have the equipment to bench‑test the PCM and replace driver modules safely.

Related Diagnostic Pages

• Dive deeper into general misfire troubleshooting with P0300.
• If you suspect an exhaust‑gas‑recirculation issue, see P0400 for a related emissions fault.

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