My Pro Street

P0357 Code: Ignition Coil “G” Primary/Secondary Circuit Malfunction

P0357 Ignition Coil G primary and secondary circuit diagnostic illustration

The P0357 code means the engine control module has detected an electrical malfunction in the primary or secondary circuit for Ignition Coil “G.”

On many coil-on-plug engines, Coil G corresponds to cylinder 7. That assignment isn’t universal, so verify the manufacturer’s coil identification before purchasing parts or dismantling the engine bay.

Common causes include a failed Ignition Coil G, damaged connector terminals, missing power, poor ground, an open or shorted PCM control wire and a failed ignition driver.

P0357 is an electrical circuit code. It isn’t simply another name for a cylinder 7 misfire, and it doesn’t automatically condemn the ignition coil.

P0357 Quick Reference

ItemInformation
OBD-II codeP0357
Official descriptionIgnition Coil “G” Primary/Secondary Circuit Malfunction
SystemIgnition-coil control
Code typeGeneric powertrain code
Commonly associated cylinderCylinder 7, but manufacturer confirmation is required
Primary faultElectrical malfunction affecting Ignition Coil G
SeverityHigh
Safe to drive?Only briefly if the engine runs smoothly
Common causesFailed coil, connector fault, damaged control wire or PCM driver failure
Typical repair rangeApproximately $75–$2,500+, depending on the cause

What Does the P0357 Code Mean?

P0357 stands for:

Ignition Coil “G” Primary/Secondary Circuit Malfunction

The powertrain control module commands Ignition Coil G to produce a spark at a precise point in the combustion cycle.

Depending on the ignition-system design, the Coil G circuit may include:

The PCM monitors electrical activity in this circuit while the engine is cranking or running.

P0357 may be stored when the PCM detects:

The exact monitoring strategy depends on the manufacturer and ignition-system design.

Which Cylinder Is Ignition Coil G?

Ignition Coil G commonly corresponds to cylinder 7 on engines equipped with one ignition coil per cylinder.

A typical assignment is:

Coil designationCommon cylinder assignment
Coil ACylinder 1
Coil BCylinder 2
Coil CCylinder 3
Coil DCylinder 4
Coil ECylinder 5
Coil FCylinder 6
Coil GCylinder 7
Coil HCylinder 8

This pattern isn’t guaranteed.

Some manufacturers assign letters according to ignition-module channels. Waste-spark systems may use one coil winding to fire two cylinders. Cylinder numbering also differs among V8 engine families.

Confirm Coil G using:

Don’t identify Coil G by assuming cylinder 7 is on a particular bank or at the rear of the engine. V8 manufacturers have been disagreeing about cylinder numbering for decades and show no signs of reaching peace.

Why Coil G Can Be Difficult to Access

P0357 commonly appears on engines with at least seven individually controlled ignition coils. That usually means a V8, V10 or V12 application.

Coil G may be located:

Rear-cylinder ignition wiring is frequently exposed to:

Inspect the wiring carefully before replacing the coil. A technician working by feel near the firewall can easily damage a connector lock or pull on the wires instead of the connector body.

What Is the Primary Ignition Circuit?

The primary circuit is the low-voltage side of the ignition coil.

It usually includes:

The PCM or ignition module allows current to build through the primary winding. This creates a magnetic field inside the coil.

When the control circuit switches off, the magnetic field collapses and induces high voltage in the secondary winding.

Primary-circuit problems include:

What Is the Secondary Ignition Circuit?

The secondary circuit delivers high voltage to the spark plug.

Depending on the system, it may include:

Possible secondary faults include:

Most modern PCMs don’t measure secondary voltage directly. They may infer secondary operation by monitoring primary current, ignition-driver feedback or changes in crankshaft speed.

How Serious Is the P0357 Code?

P0357 should be considered a high-severity code when Coil G isn’t producing spark.

A dead cylinder may send unburned fuel into the exhaust, where it can overheat and damage the catalytic converter.

Continued driving may cause:

Stop driving if:

A V8 may disguise one dead cylinder better than a four-cylinder engine. That doesn’t make the misfire harmless. It just means the engine has more coworkers available to cover the shift.

Common P0357 Symptoms

Possible symptoms include:

Some V8 engines may produce only a mild vibration or slight power loss when one cylinder stops firing. Misfire counters and scan data can reveal the problem before it becomes obvious to the driver.

Common Causes of P0357

Possible causes include:

  1. Failed Ignition Coil G
  2. Open primary coil winding
  3. Shorted primary winding
  4. Internal smart-coil electronics failure
  5. Loose Coil G connector
  6. Broken connector lock
  7. Bent or recessed terminal
  8. Spread female connector terminal
  9. Corrosion inside the connector
  10. Oil contamination
  11. Water inside the spark-plug well
  12. Missing Coil G power supply
  13. Blown ignition-coil fuse
  14. Failed ignition relay
  15. Open Coil G control wire
  16. Control wire shorted to ground
  17. Control wire shorted to voltage
  18. Excessive circuit resistance
  19. Poor Coil G ground
  20. Poor engine or PCM ground
  21. Harness damage near the firewall
  22. Wiring melted near the exhaust manifold
  23. Harness chafing against the valve cover
  24. Incorrect replacement ignition coil
  25. Damaged coil boot
  26. Excessive spark-plug gap
  27. Carbon tracking
  28. Failed ignition-control module
  29. Damaged PCM connector
  30. Failed PCM Coil G driver
  31. PCM software or calibration fault

A worn spark plug may increase secondary voltage demand and eventually damage the coil boot or internal insulation. However, spark-plug problems more commonly produce a misfire code than a direct P0357 circuit fault.

P0357 vs P0307

P0357 and P0307 may appear together, but they report different failures.

CodeMeaningDiagnostic focus
P0357Ignition Coil G primary/secondary circuit malfunctionCoil power, ground, control wiring, electronics and PCM driver
P0307Cylinder 7 misfire detectedSpark, fuel delivery, compression, airflow and mechanical condition

The P0307 Cylinder 7 misfire guide covers every major reason cylinder 7 may fail to produce normal combustion.

P0307 may be caused by:

P0357 narrows the investigation toward the electrical circuit for Ignition Coil G.

If both codes appear, diagnose P0357 first. Restoring the Coil G circuit may also eliminate P0307.

If P0307 remains after P0357 is repaired, continue testing fuel delivery, compression and the cylinder’s mechanical condition.

P0357 vs P0350

P0350 identifies a general ignition-coil primary or secondary circuit malfunction without naming one particular coil.

P0357 identifies the circuit associated with Ignition Coil G.

If P0350 appears with several individual coil codes, inspect shared components such as:

If only P0357 is stored, begin with Coil G, its connector and its individual PCM control circuit.

P0357 vs Other Individual Coil Codes

Each P0351–P0362 code applies to a different ignition-coil circuit.

My Pro Street already has dedicated coverage for:

P0357 should remain focused exclusively on the Coil G circuit.

Multiple adjacent coil codes may point toward a shared power feed, common ground, harness connector or PCM problem rather than simultaneous coil failure.

How the Ignition Coil G Circuit Works

A typical coil-on-plug ignition event works as follows:

  1. The ignition relay supplies battery voltage to Coil G.
  2. The PCM receives crankshaft and camshaft position signals.
  3. The PCM calculates ignition timing and coil dwell.
  4. The PCM sends a trigger signal or directly controls primary current.
  5. Current builds through the primary winding.
  6. The control circuit switches off.
  7. The magnetic field collapses.
  8. High voltage is induced in the secondary winding.
  9. Voltage crosses the spark-plug gap.
  10. Combustion occurs.

The PCM expects predictable voltage and current behavior.

P0357 may be stored if Coil G:

How to Diagnose the P0357 Code

1. Scan and Record Every Code

Use a capable scan tool to retrieve:

Don’t clear the codes before recording the information.

Freeze-frame data may show whether P0357 occurred:

2. Check for Related Codes

Look for:

If P0357 appears alone, suspect an individual Coil G circuit problem.

If several coil-circuit codes appeared simultaneously, inspect shared power, relay, fuse and ground circuits before replacing multiple coils.

3. Identify Ignition Coil G

Use manufacturer service information to confirm:

On a V8, verify cylinder numbering before removing engine covers or intake components.

4. Inspect Access Around Coil G

Before disconnecting the coil, inspect how the harness is routed.

Look for:

If components must be removed for access, label connectors and photograph the harness routing before disassembly.

Avoid pulling the coil connector by its wires simply because the rear of the engine has declined to provide room for fingers.

5. Inspect Coil G

Remove Coil G and inspect it for:

Inspect the spark-plug well.

Oil commonly enters through a leaking valve-cover gasket or tube seal. Repair the leak before installing another coil.

6. Inspect the Coil G Connector

Check the connector for:

Perform a terminal-drag test when appropriate.

A loose terminal may open when the engine moves under acceleration or when the harness expands with heat.

7. Inspect the Wiring Harness

Trace the Coil G circuit toward the main harness and PCM.

Pay special attention to wiring near:

Look for:

Move the harness while monitoring Coil G voltage or engine operation.

8. Check Battery and Charging Voltage

Measure battery voltage:

Low cranking voltage may interfere with ignition operation. Excessive charging voltage may damage smart-coil electronics.

Inspect battery terminals, engine grounds, chassis grounds and PCM grounds.

9. Test Coil G Power

Turn the ignition on and measure voltage at Coil G’s power terminal.

Compare it with:

If Coil G lacks power but other coils have it, inspect its connector, individual power wire and shared splice.

If several coils lack power, inspect the ignition fuse, relay and common feed.

Test the circuit under load. A high-resistance connection may show normal voltage until the coil begins drawing current.

10. Perform Voltage-Drop Testing

Measure voltage drop across:

A damaged wire may pass a continuity test while failing under operating load.

This is especially important when Coil G is at the end of a long shared power circuit or near a heat-damaged harness section.

11. Test Coil G Ground

If Coil G uses a dedicated ground, measure voltage drop between its ground terminal and battery negative while cranking or running the engine.

Compare the result with a known-good coil.

Inspect:

A poor ground may prevent the internal coil electronics from switching correctly.

12. Test the PCM Control Wire

Use the wiring diagram to identify the Coil G control circuit.

With the PCM and coil disconnected as directed, test for:

Do not use a conventional incandescent test light on the PCM control circuit unless the manufacturer explicitly approves it.

Use an LED test light, logic probe or oscilloscope intended for electronic control circuits.

13. Observe the Coil G Trigger Signal

Back-probe the Coil G control wire without damaging the connector.

Observe the signal during cranking or engine operation.

Compare it with a known-good coil.

Look for:

If Coil G receives a correct trigger but doesn’t fire, suspect the coil, power, ground or secondary path.

If the trigger is missing, test the control wire and PCM driver.

14. Perform a Coil Swap Test

If the coils are identical and accessible, move Coil G to another cylinder and install a known-good coil in its original location.

Clear the codes and reproduce the original failure conditions.

Possible results include:

A coil swap helps distinguish a failed component from a location-specific electrical fault.

15. Inspect the Spark Plug

Remove the spark plug associated with Coil G.

Check for:

Excessive spark-plug gap increases secondary voltage demand and may damage the coil boot or internal insulation.

16. Use an Approved Spark Tester

Use an adjustable or manufacturer-approved spark tester to verify Coil G output.

Disable fuel delivery when required and follow the manufacturer’s safety procedures.

Never hold a coil, plug wire or spark plug while cranking. Secondary ignition voltage may exceed 20,000 volts.

Compare Coil G output with a known-good coil under identical conditions.

17. Inspect the Primary Current Ramp

Use an oscilloscope and low-current probe to observe Coil G’s primary current ramp.

Compare it with another coil on the same engine.

Look for:

Current-ramp testing can distinguish coil failure from a weak power circuit or PCM control problem.

18. Test Under Heat

Rear-cylinder coils and connectors may experience substantial heat.

If P0357 appears after the engine warms up:

  1. Monitor the control waveform from cold.
  2. Allow the engine to reach operating temperature.
  3. Continue monitoring during heat soak.
  4. Perform a hot restart.
  5. Compare Coil G with a neighboring coil.

A coil, connector or damaged wire may operate normally cold and fail after thermal expansion.

19. Use Resistance Testing Carefully

Some conventional ignition coils have published primary and secondary resistance specifications.

Many modern smart coils don’t.

Integrated electronics may prevent meaningful resistance measurements through the external terminals. Follow vehicle-specific test procedures instead of using generic values.

20. Test the PCM Driver Last

A shorted coil or control wire can damage the PCM’s Coil G driver.

Suspect the PCM only after confirming:

Repair every external short before installing another PCM. Otherwise, the new module may immediately repeat the original failure.

Common P0357 Diagnostic Mistakes

Avoid these mistakes:

How Do You Fix the P0357 Code?

Possible repairs include:

After repairs:

  1. Clear the stored codes.
  2. Start the engine from cold.
  3. Monitor cylinder misfire counters.
  4. Verify stable Coil G power.
  5. Confirm the Coil G trigger signal.
  6. Allow the engine to reach operating temperature.
  7. Perform a hot restart.
  8. Road-test under the freeze-frame conditions.
  9. Rescan for pending codes.
  10. Confirm P0357 and P0307 don’t return.

P0357 Repair Costs

RepairEstimated cost
Diagnostic inspection$100–$300
Clean or secure connector$50–$150
Replace Coil G connector$100–$400
Repair control wiring$100–$800
Replace ignition fuse or relay$50–$250
Replace Ignition Coil G$100–$500
Replace spark plug$30–$200
Replace complete spark-plug set$150–$700
Repair plug-tube seal leak$250–$1,200
Replace ignition-control module$250–$900
Repair engine wiring harness$500–$2,500+
PCM software update$100–$300
Replace and program PCM$800–$2,500+

Costs may increase when rear-cylinder access requires removal of intake, cowl or other engine components.

Can You Drive With a P0357 Code?

Driving isn’t recommended when P0357 causes an active misfire.

A short trip may be possible if:

Stop driving if:

A V8 may continue running with one failed cylinder, but the catalytic converter still receives unburned fuel. Additional cylinders don’t make the converter more forgiving.

P0357 Frequently Asked Questions

What does code P0357 mean?

P0357 means the PCM has detected an electrical malfunction in the primary or secondary circuit for Ignition Coil G.

Is Ignition Coil G always cylinder 7?

No. Coil G commonly corresponds to cylinder 7, but manufacturers may assign coils differently. Verify the location using service information.

Does P0357 mean Coil G is bad?

Not necessarily. Connector damage, missing power, poor ground, control-wire problems and PCM driver failure can produce the same code.

Is P0357 the same as P0307?

No. P0357 identifies an Ignition Coil G electrical fault. P0307 means cylinder 7 failed to produce normal combustion.

Can a spark plug cause P0357?

An excessively worn or incorrectly gapped plug may stress the coil, but spark-plug problems more commonly cause a P0307 misfire.

Can oil in the spark-plug well cause P0357?

Yes. Oil may damage the coil boot, contaminate the connector and allow secondary ignition voltage to escape to ground.

Can exhaust heat cause P0357?

Yes. Heat may damage Coil G, its connector or nearby wiring, particularly when the coil is near the firewall or exhaust manifold.

Can wiring cause P0357?

Yes. An open control wire, short to ground, short to voltage or loose terminal can trigger P0357 while the coil remains functional.

Can a PCM cause P0357?

Yes, but PCM driver failure is less common than coil, connector and wiring faults. Test the external circuit first.

Can I swap Coil G with another coil?

Yes, if the coils are identical and the manufacturer permits it. If the fault follows the coil, the coil is likely defective. If P0357 remains, test the original circuit.

Will clearing P0357 fix it?

No. Clearing the code only resets the warning temporarily. P0357 will return if the electrical fault remains.

Final Thoughts

P0357 means the PCM has detected an electrical malfunction affecting Ignition Coil G.

Begin by confirming which coil the manufacturer designates as Coil G and which cylinder it serves. Record every code and freeze-frame value before inspecting the coil, connector, plug well and wiring.

Pay particular attention to rear-cylinder harness damage, exhaust heat, terminal tension and wiring strained by limited access.

Verify Coil G power and ground, then compare its control pulse and primary current ramp with a known-good coil. A coil swap can confirm an internal failure, but P0357 remaining at the original circuit points toward the connector, control wire or PCM driver.

Test the PCM last and repair any shorted coil or wiring before installing a replacement module.

For additional diagnostic coverage, visit the complete P-series OBD-II code guide, browse the OBDII Doctor archive or continue with the P0307 Cylinder 7 misfire guide.

P0357 identifies the circuit. Accessing it may still require three extensions, two universal joints and language not approved by the service manual.

Exit mobile version