P0679
Cylinder 9 Glow Plug Circuit/Open
Glow plug / diesel preheat
Generic OBD-II
Medium
What it means
P0679 means the diesel engine's computer has detected an open (broken) circuit for the cylinder 9 glow plug. Glow plugs warm the combustion chamber to help the engine light off, so this fault mainly causes harder, rougher, smokier cold starts rather than stopping the engine from running once it is warm.
Medium
Can I keep driving? Usually yes — the engine still starts and runs, but cold starts get harder and rougher until the cylinder 9 glow plug circuit is fixed.
Common symptoms
What you'll notice
- Hard starting in cold weather
- Glow plug or check-engine light on
- Rough idle and white smoke right after a cold start
- Reduced cold-engine performance
Common causes
Most likely first
- Burned-out (open) cylinder 9 glow plugLikely
- Open or broken wiring/connector in the glow plug circuitCommon
- Loose or corroded electrical connectionCommon
- Faulty glow plug control moduleLess often
How to diagnose & fix
Work through it in order
- Scan and confirm P0679, then check for other glow plug codes.
- Measure the cylinder 9 glow plug resistance; an open reading confirms a failed plug.
- Inspect the wiring and connector for breaks, corrosion, or looseness.
- Replace the failed glow plug or repair the open wiring.
- If those are good, test the glow plug control module and its power feed.
FAQ
Quick answers
Is it safe to drive with P0679?+
Usually — the engine runs on its other cylinders, but cold starts suffer. Repair it before cold weather for reliable starting.
Can I just clear P0679?+
It will come back after the next glow-plug self-test unless the open plug or wire is repaired.
Related codes
Often seen with P0679
Read & clear P0679 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