P0670: Glow Plug Control Module Control Circuit
The engine control unit has detected a fault in the glow plug control module circuit.
Normal risk
Usually drivable. Cold starts may be harder.
Short answer · Can I keep driving with P0670?
Yes, in mild weather. In cold weather starting may be hard. Have the glow plug module checked before winter.
What does P0670 mean?
Code P0670 means the control circuit between the engine control unit and the glow plug control module has a fault.
The control module itself, its fuse, wiring or connector can be at fault. The engine control unit cannot switch the glow plugs reliably.
What the car does when the code is set
The glow plug or check engine light comes on or flashes. The car drives normally, but in cold weather it may need longer cranking, run roughly for the first minutes and produce white smoke until it warms up.
How the system works
Diesel engines ignite their fuel by compression heat alone. In cold weather the cylinder walls absorb so much heat that the air may not get hot enough, so each cylinder has a glow plug that heats the combustion chamber before and just after starting. A glow plug control module switches them on for a period set by the engine control unit, and on many engines also keeps them on after starting to reduce smoke and noise. The module monitors the current in each plug circuit and reports faults back to the engine control unit.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Failed glow plugA plug with an open circuit.
- Faulty glow plug control moduleThe module or relay that powers the plugs fails.
- Wiring or connector faultLoose or corroded terminals on the plugs.
- Fuse faultA blown high-current fuse for the glow system.
How it is diagnosed
- Read the module dataMany control units show which glow plug circuit failed.
- Measure each plugWith the wiring removed, measure each plug's resistance. An open circuit means it needs replacing.
- Check the module and fuseCheck power, ground and control signal to the module.
- Replace plugs carefullyGlow plugs can seize. Remove them with the engine warm and the correct torque to avoid breaking them.A broken glow plug in the cylinder head is expensive to remove. If one feels stuck, stop and seek a workshop.
Questions about P0670
Can a blown fuse set P0670?
Yes. Check the high-current glow system fuse first.
Can I drive with a glow plug code?
Yes, in mild weather the engine usually starts. In cold weather starting gets harder and it may smoke white for a while after starting.
How long do glow plugs last?
Often over 100,000 km, but this varies a lot by engine. Some manufacturers recommend replacing them all at the same time.