P0677
Cylinder 7 Glow Plug Circuit/Open
Glow plug / diesel preheat
Generic OBD-II
High
What it means
P0677 is a diesel code meaning the ECM has found an open circuit in the glow plug for cylinder 7. Glow plugs pre-heat the combustion chamber for cold starting, so a single open plug mainly causes hard cold starts and rough, smoky running until the engine warms up — it does not affect a warm engine.
High
Can I keep driving? You can usually drive once warm, but expect hard cold starts and rough cold running until the glow plug circuit is repaired.
Common symptoms
What you'll notice
- Hard or slow starting when cold
- Rough idle and white smoke on a cold start until warm
- Glow plug (coil) warning light or check-engine light on
- Reduced power in cold weather
Common causes
Most likely first
- Failed (open) glow plug on cylinder 7Likely
- Open or shorted wiring/harness to the cylinder 7 glow plugCommon
- Corroded or loose electrical connectorCommon
- Faulty glow plug control moduleLess often
- Faulty ECM/PCM driver (less common)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the fault is on cylinder 7.
- Measure the cylinder 7 glow plug resistance — an open plug reads infinite and needs replacing.
- Inspect the harness and connector for an open circuit or corrosion.
- Check the glow plug control module output and its power/ground.
- Repair the open, clear the code, and retest a cold start.
FAQ
Quick answers
Is it safe to drive with P0677?+
Usually yes once warm, but cold starts will be difficult and it may run rough and smoke. It's not an emergency, but fix it before cold weather.
Can I just clear P0677?+
It will come back the next time the ECM checks the glow plug circuit. The open plug or wire has to be fixed for the code to stay away.
Related codes
Often seen with P0677
Read & clear P0677 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