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P0670 OBD-II Trouble Code: Glow Plug Module Control Circuit

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P0670 code definition

If your vehicle’s ECM detects a problem with the Glow Plug Control Module (GPCM) control circuit, this code gets stored.

What the P0670 code means

Unlike gas engines, diesel engines don’t use sparkplugs for ignition. Instead, they rely on glow plugs for this important task. As the name would suggest, the Glow Plug Control Module is a big part of this. If it isn’t working correctly, your engine may not start.

What causes the P0670 code?

One problem could simply be the GPCM itself. A defective GPCM will set off this code all on its own. Other common issues that lead to a P0670 code are:

  • GPCM harness that’s shorted or open
  • GPCM circuit that’s suffering from a poor electrical connection
  • The ECM isn’t working correctly (this is pretty rare)

What are the symptoms of the P0670 code?

The most obvious problem related to this code is that your diesel engine simply won’t start. At the very least, it will most likely hesitate before coming to life. Usually, if the weather is warm, even a P0670 code shouldn’t stop your vehicle from starting. However, if it’s cold out, you’ll probably have a lot more trouble getting going.

Even if the engine does start, you will most likely hear a very loud knocking noise coming from it. This will continue until the engine warms and is able to function normally within an acceptable operating temperature.

White smoke may also come out of your vehicle’s exhaust. This is because the hard start produces excess fuel that must be burned off. The engine will have a noticeable miss before the cylinder head temperature increases enough to sustain total combustion.

How does a mechanic diagnose the P0670 code?

First, your mechanic will use their OBD-II scanner to diagnose which codes have been stored. Then, they’re going to check to see if your battery is working. Next, they’ll inspect the wiring, looking for any defects that may lead to the GPMC not getting the power it needs to work properly. A voltmeter helps with this.

After all that, they’re going to check to see if the ignition switch delivers power. They’ll do the same with the relay actuation by unplugging the oil temperature sensor and then hitting the ignition.

Common mistakes when diagnosing the P0670 code

The biggest mistake mechanics make when this code is present is going right to replacing the glow plug. As it’s the most obvious feature of the problem, many people assume it’s simply not working. Although a brand new glow plug may function better at first, if you don’t address the underlying problems, it will only be a matter of time before you need to see a mechanic again.

How serious is the P0670 code?

Your life won’t be in danger when the P0670 code is stored. Likewise, it’s not going to lead to any serious damage to your vehicle. However, until this problem is fixed, you are in for a terrible time with your ignition. So, in that regard, this is a very serious issue that should be addressed right away.

What repairs can fix the P0670 code?

Your mechanic may do any of the following:

Additional comments for consideration regarding the P0670 code

Just because your diesel engine needs a couple extra seconds to start in the cold doesn’t mean your GPMC or glow plug need to be replaced or repaired.

Need help with a P0670 code?

At YourMechanic, we have an army of certified mobile mechanics ready to rescue you from the P0670 code and all kinds of other problems that can impact your vehicle. All you have to do is fill out this online form and we’ll quickly reply with a quote before scheduling an appointment. You can also call 1-800-701-6230 to speak with a service advisor about a good time and date for repairs. Our mechanics will happily meet you at your home or workplace.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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