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P0357 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

P0357 is an OBD-II Code that means Ignition Coil G primary/secondary circuit malfunction. The power transistor isn't getting the correct voltage to trigger the coil. 

Meaning

A P0357 code is the result of the ECM (Engine Control Module) receiving a signal from the PCM (Powertrain Control Module) to check the coil control circuit. The PCM monitors the voltage from the coil to tell when it's ready to fire. If the coil control circuit is malfunctioning, the ECM sets a P0357 code and turns on a Check Engine Light. 

Causes

Common causes for this code include:

  • Open/Short in the wire between the PCM and coil 
  • Open/Short in the wire between the Coil and Ignition Coils.
  • Faulty Ignition Coil or Coil pack 
  • Faulty Power transistor (Sometimes called a 'Driver' transistor)
  • Open/Short in main Power Supply 
  • Faulty ECM

Symptoms

Symptoms of P0043 can include any or all of the following:

  • Engine may surge or hesitate when turning on or accelerating from a stop; during deceleration, the engine may misfire and stumble.
  • Malfunction Indicator Lamp (MIL) Illuminated (a.k.a., Check Engine Light)
  • Vehicle may enter "Limp Mode" 
  • Possible increased power demand from the PCM to activate the coil
  • Vehicle may vibrate and the engine could make noises

Diagnosis

To diagnose a P0043 DTC code, a certified mechanic will use an advanced code scanner to check the freeze frame data of the vehicle. The mechanic should also perform a cylinder balance test on cylinders 1 through 6 to check for misfiring or damage. If the coil under examination proves bad by exhibiting high resistance, replace it with a new one of the same part number.

An oscilloscope, a scanner, and an ohmmeter are most likely to be used by the mechanic. This will allow them to determine the voltage that is causing the issue. They'll also check the coil itself and, if necessary, other components.

They'll also most likely conduct a visual examination of the other electrical components. If the engine has been misfiring, they'll need to inspect it to determine if this issue is connected or caused by something else. They may do so by gradually increasing the RPMs while observing whether a backfire occurs.

Common mistakes

The following are common mistakes when diagnosing the trouble code P0357: 

  • Replacing the coil(s) without determining if they are bad. 
  • Replacing the wrong part. If you replace both coils on a four-cylinder engine, make sure to buy two identical coils, or else you may have spark issues elsewhere with your car.
  • Not replacing with OEM parts 
  • Forgetting to check all other electrical components before replacing the coil(s)
  • Replacing just one of the coils when there are 2 or more that need to be replaced 
  • Forgetting to plug in the distributor if applicable 
  • Assuming it's another code, such as P0341, rather than this one

Points to Note: When diagnosing a P0357 code, it's important to be sure what type of code you're dealing with. There are two types of ignition coils: low impedance and high impedance. Low-Impedance coils can cause a code like P0357 while High-Impedance coils will set a different code. For example; if the coil is shorting out it may set a code for Ignition Coil C (P0325) and not P0357. Further testing would need to be done to determine if this is the case. 

It's also possible to check for codes on both types of coils, so you should be aware that if your coil is shorting out, it's possible to get a "misfire detected" code even though there isn't actually misfire happening since the ECM can detect current flow through a shorted coil. In this case, it will set a P0325 code on either type of coil. 

Another important factor to consider is what the vehicle's symptom was when the problem occurred. If you have an engine miss at idle and a misfire detected light on, then a good bet would be to check the ignition coil number 2 (Primary). If you're not sure exactly which number is the primary ignition coil for your vehicle, there should be a good indication on the wiring harness.

How serious is this?

A car with a P0043 trouble code stored in its engine controller is not able to operate at full power. The code will turn on a Malfunction Indicator Lamp (MIL) and can prevent the vehicle from "going into limp mode." This may cause the engine to stall at intersections or when coming to a stop. You can clearly see why this may be less than ideal. 

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Replace ignition coils 
  • Completely replace the power transistor
  • Replace the PCM 
  • Repair or replace wiring and/or connectors that could be causing the problem 
  • Test for Open Circuit in Ignition Coil C Primary (if applicable) 
  • Test for Open Circuit in Ignition Coil C Secondary (if applicable)

Warning! The following are actions you should NOT take when repairing the code:

Moving wires or connectors that could be corroded. For instance, if this issue is happening on one cylinder but not all cylinders, don't just move the wire to another ignition coil. This could create an electrical short and cause further issues with your car. Moving any part without completely understanding why it was failing can lead to additional problems. Don't replace parts until you're 100% satisfied that they're the source of the trouble. Replacing parts without fully diagnosing them can also cost considerably more than what it would have originally run for a simple diagnosis.

Related codes

P0325 - Ignition Coil C Primary Open Circuit

P0326 - Ignition Coil C Primary Short to Ground

P0335 – Ignition Coil C Secondary Open Circuit

How much does it cost to fix the P0357 code?

Repairs for this code typically cost between $100 and $400. The cost will vary depending on the exact issue causing the code, if other codes are being set at the same time, what part(s) need to be replaced, how many parts are needed to complete the repair, labor rates in your area, and any discounts you may qualify for. Replacing coils can typically cost between $50 and $200 while replacing an entire distributor assembly can run around $250.

Conclusion

In conclusion, the P0357 is a trouble code that is basically triggered by the failure of an ignition coil or switches that control it. It's a serious issue that can cause the vehicle to run poorly or even stall at intersections.

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