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P0670: Glow plug module control: circuit fault

The ECU has found a fault in the circuit that commands the diesel glow plug module or relay, usually noticed as poor cold starting.

Code P0670 at a glance
CodeP0670
SystemEngine and transmission
GroupP06xx, Control unit and auxiliary outputs
TypeGeneric: it means the same on every make
Can you keep driving?With care

What P0670 means

Diesel engines use glow plugs to heat the combustion chamber so the engine starts easily from cold. The ECU does not power them directly: it signals a module or relay, which sends them the current. This code means the ECU sees something wrong on that control circuit, such as a break, a short or a response that does not add up.

Most common causes

  • Blown glow plug fuse
  • Loose or corroded connector at the module or relay
  • Damaged control wire between the ECU and the module
  • One or more shorted glow plugs that have overloaded the module
  • Faulty glow plug module or relay
  • ECU fault (uncommon)

Symptoms

  • Hard or slow starting from cold
  • White smoke and diesel smell on start-up
  • Rough running for the first few seconds
  • Glow plug warning light (the coil symbol) flashing or not lighting

Can you drive with P0670?

With care Once warm the car drives normally, but on cold days it can be very hard to start or refuse to start. Best fixed before the weather turns cold.

How to check it

With the engine cold, switch the ignition on and watch the coil-shaped light: it should come on for a few seconds and go out. A garage can check whether current reaches the glow plugs during preheating.

How to read and clear P0670 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0670 with this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

P0670 is a generic code, so it means the same on any make, for example on Citroën, Hyundai, Mercedes-Benz, Mini, Renault, Volvo. See what Final OBD does on your car in makes and models.

What does code P0670 mean?

Diesel engines use glow plugs to heat the combustion chamber so the engine starts easily from cold. The ECU does not power them directly: it signals a module or relay, which sends them the current. This code means the ECU sees something wrong on that control circuit, such as a break, a short or a response that does not add up.

Can you drive with P0670?

Once warm the car drives normally, but on cold days it can be very hard to start or refuse to start. Best fixed before the weather turns cold.

How do you clear P0670?

With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0670 comes back.