P0357 is an ignition coil circuit trouble code that can make your engine run rough, trigger the check engine light, and even cause hard starting. It points to a problem with the ignition coil “G” primary/secondary circuit, which is usually cylinder #7 on V8 engines. While the code sounds intimidating, you can usually narrow it down to a bad coil, wiring fault, or sometimes a driver issue inside the ECU. In this guide, you’ll learn what P0357 means, common causes, symptoms, and realistic repair options.
What Does P0357 Mean?
P0357 is an OBD-II diagnostic trouble code that stands for “Ignition Coil ‘G’ Primary/Secondary Circuit Malfunction.” On most V8 engines, coil “G” corresponds to cylinder #7. Your ECU monitors the electrical signal going to and from each ignition coil. When it detects a voltage pattern that’s out of range on the #7 coil circuit, it sets P0357 and usually turns on the check engine light.
This code can be triggered by a failed ignition coil, damaged wiring or connectors, poor power/ground, or in less common cases, a faulty ECU driver. Because it affects spark on one cylinder, you’ll often feel a misfire under load or at idle.
Quick Reference
- Code: P0357
- Definition: Ignition Coil “G” (typically cylinder #7) primary/secondary circuit fault
- Severity: Moderate to high – misfire risk and possible catalytic converter damage
- Most common fix: Replace ignition coil on affected cylinder, repair wiring if needed
- Driveability: Often runs rough; driving for long with this code is not recommended
Real-World Example / Field Notes
In the shop, I see P0357 most often on V8 trucks and SUVs with coil-on-plug setups. A typical case: a customer comes in with a flashing check engine light under acceleration and rough idle. Scan tool shows P0357 and sometimes a misfire code for cylinder 7. Swapping the #7 coil with another cylinder moves the misfire and the code, confirming a bad coil. Other times, especially on higher-mileage vehicles, I’ll find a cracked coil connector or rubbed-through harness near the valve cover causing intermittent loss of signal.
Symptoms of P0357
- Check engine light – steady or flashing, often appears under load or during acceleration.
- Engine misfire – noticeable stumble, shaking at idle, or hesitation when you step on the gas.
- Rough idle – engine may feel uneven, with RPMs slightly hunting or vibrating more than normal.
- Loss of power – reduced acceleration, especially when climbing hills or towing.
- Poor fuel economy – unburned fuel from the misfiring cylinder leads to more frequent fill-ups.
- Hard starting – in some cases, extended cranking or needing more throttle to start.
- Exhaust smell – strong fuel smell from the tailpipe due to incomplete combustion.
- Possible catalytic converter stress – prolonged misfire can overheat and damage the converter.
Common Causes of P0357
Most Common Causes
- Failed ignition coil on cylinder #7 – internal short, open winding, or breakdown under heat.
- Damaged coil connector – loose pins, broken lock tabs, or corrosion causing poor contact.
- Wiring issues to coil #7 – chafed, broken, or pinched wires between the coil and ECU.
- Poor power or ground – weak battery power, bad engine ground, or shared power feed problems.
- Oil or moisture intrusion – valve cover leaks or water in the plug well causing arcing and coil failure.
Less Common Causes
- Faulty ECU/PCM driver – internal failure of the ignition driver circuit for coil “G.”
- Aftermarket performance parts – poorly matched coils, plugs, or tuners affecting coil control.
- Spark plug issues – severely worn or cracked plug on cylinder #7 stressing the coil circuit.
- Previous repair damage – harness stretched or pinched after engine work or plug replacement.
- Rodent damage – chewed wiring near the coil or along the valve cover.
Diagnosis: Step-by-Step Guide
You’ll ideally have a basic scan tool, a digital multimeter, and access to wiring diagrams. A bidirectional scan tool with Mode $06 data and misfire counters is even better, but not mandatory for a home diagnosis.
- Confirm the code and check for companions. Scan for P0357 and look for related misfire codes (like P0307) or other coil circuit codes. Note freeze-frame data (RPM, load, temperature) to see when the fault occurs.
- Perform a quick visual inspection. With the engine off, locate the #7 ignition coil (often rear of the engine on one bank). Check for cracked coil housings, broken connectors, loose plugs, or obvious harness damage.
- Swap coils between cylinders. Move the #7 coil to another cylinder and move that cylinder’s coil to #7. Clear the codes and test drive. If the code or misfire follows the coil, the coil itself is bad.
- Inspect the spark plug on cylinder #7. Pull the plug and check for fouling, cracks, excessive gap, or oil contamination. Replace if worn or questionable, and make sure the plug well is clean and dry.
- Check coil power and ground. With the key on, use a multimeter or test light to verify 12V supply at the coil connector and a solid ground. Compare readings with a known-good cylinder.
- Test the signal wire from ECU. Using a wiring diagram, identify the control wire for coil “G.” With the engine cranking or running, use a test light or scope (if available) to confirm the ECU is pulsing the coil. No signal may indicate a wiring or ECU issue.
- Wiggle test the harness. While the engine is idling, gently move the wiring harness near coil #7 and along the route to the ECU. If the engine stumbles or the code sets intermittently, you likely have a broken or internally damaged wire.
- Check Mode $06 and misfire data (if available). Some scan tools show cylinder-specific misfire counts and coil test results. High misfire counts on cylinder 7 support a coil, plug, or wiring issue on that cylinder.
- Inspect for ECU issues (last resort). If the coil, plug, power, ground, and wiring all test good, and there’s no control signal from the ECU, you may be dealing with a failed ignition driver inside the ECU. This usually requires professional testing and replacement or repair of the module.
Pro tip: Always fix any oil leaks into the spark plug tubes before installing new coils or plugs. Otherwise, the new parts can fail early and bring P0357 right back.
Possible Fixes & Repair Costs
The exact repair for P0357 depends on what you find during diagnosis, but most fixes are straightforward ignition or wiring work. Parts prices vary by brand and engine, and labor rates differ by region and shop type.
- Replace ignition coil on cylinder #7: The most common repair. Parts typically $40–$150 per coil; labor $50–$150 depending on access. Many owners replace the spark plug at the same time.
- Replace spark plug on cylinder #7: Plug costs $8–$25 each; labor $50–$150 depending on engine layout. Often done with coil replacement as preventative maintenance.
- Repair or replace coil connector: Pigtail repair kits usually $15–$40; labor $80–$200 depending on how much harness work is needed.
- Repair damaged wiring harness: Small section repair can be $100–$300. Larger harness replacement or extensive rodent damage can reach $400–$800+.
- ECU/PCM repair or replacement (rare): Used or reman units generally $250–$800 plus programming; labor $150–$400. This is the last thing you replace after verifying everything else.
Overall, most P0357 repairs fall in the $150–$450 range when it’s just a coil and plug, and can climb higher if wiring or ECU problems are involved. Access difficulty, shop labor rate, and OEM vs aftermarket parts are the main factors affecting cost.
Can I Still Drive With P0357?
You can often still drive with P0357, but it’s not a good idea to keep doing so. A single-cylinder misfire might feel like just a rough idle or lack of power, but unburned fuel is going straight into the exhaust. That can overheat and damage the catalytic converter, which is far more expensive than a coil. If the check engine light is flashing, that’s the ECU warning you about active misfire – you should reduce load immediately and get the vehicle checked as soon as possible.
What Happens If You Ignore P0357?
Ignoring P0357 can turn a relatively simple ignition repair into a much larger bill. Long-term misfire can melt or clog the catalytic converter, foul oxygen sensors, and contaminate engine oil with fuel. You’ll also deal with poor performance, higher fuel consumption, and the risk of stalling at the worst possible time.
Related Codes
- P0399 – Ignition Coil “R” Primary/Secondary Circuit
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
- P0355 – Ignition Coil “E” Primary/Secondary Circuit
Key Takeaways
- P0357 points to an electrical problem in the ignition coil circuit for coil “G,” usually cylinder #7 on V8 engines.
- Most cases are caused by a bad ignition coil, damaged connector, or wiring fault, not an ECU failure.
- Symptoms include check engine light, misfire, rough idle, loss of power, and poor fuel economy.
- Diagnosing involves coil swapping, checking power/ground, inspecting wiring, and verifying ECU signal.
- Typical repairs run from about $150–$450 for coil and plug replacement, more if harness or ECU work is needed.
- Driving long-term with P0357 risks catalytic converter damage and higher overall repair costs.
Vehicles Commonly Affected by P0357
P0357 shows up most often on V8 engines with coil-on-plug ignition systems. In the field, it’s common on:
- Ford F-150, Expedition, Explorer, Mustang, and other 4.6L, 5.0L, and 5.4L V8 engines.
- Chevrolet/GMC Silverado, Sierra, Tahoe, Suburban, Yukon, and other 4.8L, 5.3L, and 6.0L V8s.
- Dodge/Ram trucks and SUVs with 4.7L, 5.7L HEMI, and similar V8 engines.
- Toyota/Lexus Tundra, Sequoia, Land Cruiser, and LS/GS models with V8 coil-on-plug setups.
- Other V8 platforms from Nissan/Infiniti, BMW, and Mercedes-Benz where each cylinder has its own coil.
That said, any OBD-II vehicle with individually controlled ignition coils can set P0357 if the #7 coil circuit has an issue.
FAQ
Can I clear P0357 and keep driving if the car feels okay?
You can clear the code, but if the underlying problem is still there, P0357 will come back. Even if the engine feels “okay,” a weak or intermittent coil can cause hidden misfires that stress the catalytic converter. It’s better to diagnose and fix the cause rather than repeatedly clearing the light.
Is P0357 always the ignition coil itself?
No. The coil is the most common failure, but not the only one. A broken connector, damaged wiring, poor ground, or even an ECU driver fault can all trigger P0357. Swapping coils between cylinders is a quick way to confirm if the coil is actually the culprit.
How do I know which cylinder is #7 on my engine?
Cylinder numbering depends on the manufacturer and engine design. On many American V8s, cylinder 1 starts at the front of one bank and numbers run to the rear. Cylinder 7 is usually the rear cylinder on the driver’s side, but you should always verify with a service manual or reliable diagram for your specific engine.
Can a bad spark plug cause P0357?
A bad spark plug doesn’t directly cause the circuit code, but a severely worn or shorted plug can overload the coil and contribute to coil failure. When a coil fails electrically because it’s been overworked, the ECU may see abnormal voltage in the coil circuit and set P0357. That’s why it’s smart to inspect or replace the plug when dealing with this code.
How urgent is it to fix P0357?
You should address P0357 as soon as you reasonably can. A short drive to a shop is usually fine, but extended driving with an active misfire can damage the catalytic converter and other components. If the check engine light is flashing, treat it as urgent and avoid heavy acceleration or towing until it’s repaired.