P06C8
Cylinder 4 Glow Plug Incorrect
Glow plug / diesel preheat
Generic OBD-II
High
What it means
P06C8 is a diesel code meaning the control module measured the cylinder 4 glow plug and found its electrical characteristics don't match what it expects — commonly a wrong or non-spec plug fitted, or one whose resistance has drifted out of range. Glow plugs preheat the cylinder for starting, so the main effects are hard cold starts and rough, smoky running until the engine warms.
High
Can I keep driving? Usually drivable — expect hard cold starts and rough, smoky running until warm; a single mismatched glow plug rarely stops the engine from starting.
Common symptoms
What you'll notice
- Hard starting when the engine is cold
- Rough running or misfire until the engine warms up
- White or grey exhaust smoke on cold starts
- Check-engine or glow-plug warning light on
Common causes
Most likely first
- Wrong-specification glow plug fitted to cylinder 4Likely
- Faulty cylinder 4 glow plug (out-of-range resistance)Common
- Wiring or connector fault at the cylinder 4 glow plugCommon
- Faulty glow plug control moduleLess often
How to diagnose & fix
Work through it in order
- Confirm the correct glow plug part number for the engine and check that cylinder 4 has the right plug fitted.
- Measure the cylinder 4 glow plug's resistance and compare it to the others.
- Replace the plug with the correct-spec part if it is wrong or out of range.
- Inspect the wiring and connector, and test the control module output if needed. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P06C8?+
Generally yes, but cold starts will be harder and the engine may run rough and smoky when cold until the plug is corrected.
Can I just clear P06C8?+
It will return when the module re-checks the plug. If the wrong glow plug was fitted, it needs to be swapped for the correct part.
Related codes
Often seen with P06C8
Read & clear P06C8 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