P0357 OBD-II Trouble Code: Ignition Coil G Primary/Secondary Circuit Malfunction

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Cost of diagnosing the P0357 code

P0357 is a diagnostic trouble code (DTC) for "Ignition Coil G Primary/Secondary Circuit Malfunction". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

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P0257 code definition

When the P0257 code is stored, it means that the PCM has detected one or more ignition coils is faulty to some degree.

What the P0257 code means

Most vehicles with an OBD-II system utilize a “coil on plug” (COP) method of providing the necessary ignition spark for the engine to work. In this type of system, the coil is secured to the engine in a specific way so that a plug boot or spark plug wire can be used for ignition. The PCM electronically controls these ignition coils.

The P0257 code actually relates to the electrical circuitry that connects the PCM to the ignition coil(s). Typically, a pulsing ground provided by the PCM and a supply of voltage from the battery is sent to the ignition.

Any voltage that is registered at greater than the manufacturer’s standards by more than 10% will trigger the code. The PCM may even shut down the associated fuel injector. This code is usually associated with ignition coil number seven.

What causes the P0257 code?

There are a few things that could be responsible for this code:

  • Wildlife chewing through wires or otherwise interrupting their performance
  • Faulty ignition coils
  • Open or shorted wiring in the ignition coil driver circuit
  • PCM failure (this is very rare)
  • A bad coil
  • A power control module that is faulty
  • Faulty connector locks
  • A bad connection at the coil
  • A COP driver circuit that is open
  • The ECM is faulty

What are the symptoms of the P0257 code?

When the P0257 code is triggered, you should see your Check Engine Light come on. You’ll most likely also notice a sudden lack of power as this problem directly affects an ignition coil. Your engine may hesitate when you turn it on or try to accelerate. Even when you’re simply idling, your car may vibrate and the engine could make noises.

How does a mechanic diagnose the P0257 code?

To diagnose the problem regarding a P0257 code, your mechanic will most likely use an oscilloscope, along with a scanner and an ohmmeter. This will allow them to measure the voltage that’s causing the problem. They’ll also inspect the coil itself and, potentially, the others too.

Furthermore, they will most likely carry out a visual inspection of the other electrical components as well. If the engine has been misfiring, they’ll also need to examine it to see if this problem is related or caused by something else. They can do this by slowly raising the RPMs while the vehicle is kept stationary and seeing if the backfire occurs.

Common mistakes when diagnosing the P0257 code

A lot of times, a simple maintenance tune-up is prescribed to fix this problem. While it may very well have been high time for this kind of attention, a thorough diagnosis should always be carried out first to find the true root of the malfunction. Simply assuming is how a mechanic can spend a lot of time and bill a lot of money without actually fixing anything.

How serious is the P0257 code?

You’ll have a difficult time getting around as long as this code is present. While your life isn’t at risk, the health of your car probably is.

What repairs can fix the P0257 code?

Your mechanic may need to do any of the following:

Additional comments for consideration regarding the P0257 code

In some rare cases where the problem seems to be an intermittent condition, it can be very difficult to find the true source of the code. Sometimes, the problem simply has to get worse before it can be properly diagnosed.

Need help with a P0257 code?

YourMechanic is happy to provide certified mobile mechanics to customers struggling with a P0257 code. We can dispatch a certified mobile mechanic to your home or office where they’ll diagnose the problem and even carry out necessary repairs so you can get back on the road right away. Just call us at 1-800-701-6220 to speak with a service advisor or you can simply fill out this form. Our expert technicians will reply with a quote and get your preferred time and date for an appointment.

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