What to do about a P0670 fault code
Leave P0670 into the colder months and a diesel can refuse to start on a frosty morning. The code points to the module that switches the glow plugs, and we can test it at your home or workplace.
Can you keep using it with P0670?
Fine for now
In mild weather a warm diesel usually starts and runs normally without its glow plugs, so day-to-day use is generally fine.
Get it booked this week
If cold starts are getting slower or the engine runs rough for the first minute, book a check before the weather turns.
Stop and call us
Call if the engine won't start at all. Repeated long cranking flattens the battery and strains the starter motor.
Signs that go with P0670
- Slow or difficult starting from cold
- White smoke and a rough idle until the engine warms up
- A glow plug light that flashes or stays on, on some makes
What P0670 means
The official definition is Glow plug control module circuit. The ECU talks to a separate module or relay that powers the glow plugs, and it has found a fault in that module's circuit, so it can't be sure the plugs are being heated.
Common causes
A failed glow plug control module or relay
The module switches heavy current, and it can fail with age or after a glow plug shorts out.
Wiring or connector faults
A corroded plug or damaged wire between the ECU and module breaks the control signal.
A blown fuse or poor supply
Without its power feed, the module can't respond to the ECU.
What to do right now
- Note how the engine starts from cold, and whether the glow plug light behaves oddly.
- Keep the battery healthy. Avoid long cranking, and give it a few seconds between attempts.
- Don't keep clearing the code, as it comes straight back on the next cold start.
- Book a check before cold weather sets in.
How we sort P0670 where the vehicle is parked
We read the codes and test the control module's supply, signal and output to the glow plugs for £100 + VAT. That tells you whether it's the module, its wiring or a fuse, and a garage fits any new part using our findings.
A faulty plug can take a module out with it, so we check for that too, with P0380 often stored alongside. If the vehicle won't start, mention it when you book.
Reviews
Will P0670 put the car into limp mode?
Rarely. The effect is on starting and cold running, not on power once the engine is warm.
How long can I leave P0670 before it gets worse?
In summer, a while. As temperatures drop, starting gets harder and a no-start becomes likely.
Can P0670 damage the engine?
Not usually, but repeated hard starts wear the starter and battery, and long rough running from cold isn't kind to the engine.
Will my car pass its MOT with P0670 showing?
Not while the engine light is on, so get the fault fixed first.
Is P0670 something I can fix myself?
Checking the fuse is reasonable. Testing the module needs a meter and live data.
Get P0670 looked at where the vehicle is parked
Tell us how the vehicle starts and where it's parked, and we'll come out and test the glow plug system.
More fault codes explained
Eccles, Manchester M30 0SF