P0670
Glow Plug Control Module 1 Control Circuit/Open
Glow plugs (diesel)
Generic OBD-II
High
What it means
P0670 is a diesel code meaning the ECM has detected an open in the control circuit for the glow plug control module. Glow plugs pre-heat the cylinders so a cold diesel will light off; when the module's circuit is open, that pre-heating fails and cold starts become hard, smoky, and rough. It normally points at the module or its wiring, not at the engine internals.
High
Can I keep driving? The engine usually still runs, but cold starts can be hard, smoky, and rough until the glow-plug system is fixed — worse the colder it gets.
Common symptoms
What you'll notice
- Check-engine light on (and often a glow-plug/wait-to-start light)
- Hard starting, especially in cold weather
- Rough running and white exhaust smoke on a cold start
- Misfire-like shake until the engine warms up
Common causes
Most likely first
- Faulty glow plug control moduleLikely
- Open or damaged wiring/connector in the module's control circuitCommon
- Corroded or loose glow-plug harness connectionsCommon
- Failed engine control module (ECM) driving the glow-plug moduleLess often
How to diagnose & fix
Work through it in order
- Scan and record freeze-frame data, then confirm whether the module or its control wiring is open.
- Inspect the glow-plug control module connector and harness for corrosion, damage, or an open circuit; repair as needed.
- Check the module's power and ground feeds before condemning the module itself.
- If wiring and feeds are good, replace the glow plug control module and re-test cold-start behaviour.
FAQ
Quick answers
Is it safe to drive with P0670?+
You can usually drive once started, but cold starts will be hard and smoky. Fix it before winter, since a dead glow-plug system can leave you unable to start on a cold morning.
Can I just clear P0670?+
It clears, but returns as soon as the module or its wiring fails again. Repair the open circuit first.
Related codes
Often seen with P0670
Read & clear P0670 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX