P0678
Cylinder 8 Glow Plug Circuit/Open
Glow plugs (diesel)
Generic OBD-II
High
What it means
P0678 is a diesel code meaning the control module detected an open (broken) circuit for cylinder 8's glow plug. Glow plugs preheat the combustion chamber for cold starting, so a failed plug or broken wire here shows up mainly as hard cold starts and rough running until the engine warms.
High
Can I keep driving? Usually driveable, but expect hard cold starts and rough cold running; a warm diesel will normally still run on the remaining cylinders.
Common symptoms
What you'll notice
- Difficulty starting, especially in cold weather (long crank)
- Rough running or a temporary miss until the engine warms up
- White or grey exhaust smoke on a cold start
- Check-engine or glow-plug warning light on
Common causes
Most likely first
- Failed cylinder 8 glow plug (open circuit)Likely
- Open or broken wiring in the cylinder 8 glow plug circuitCommon
- Loose or corroded electrical connector at the glow plugCommon
- Faulty glow plug control moduleLess often
How to diagnose & fix
Work through it in order
- Scan and confirm the code is for cylinder 8, and read freeze-frame data.
- Inspect the cylinder 8 glow plug wiring and connector for an open, breakage, or corrosion.
- Measure the glow plug's resistance; an open (infinite) reading means the plug has failed — replace it.
- Verify the glow plug control module is powering the circuit before replacing it.
- Repair, clear the code, and do a cold start to confirm the fix.
FAQ
Quick answers
Is it safe to drive with P0678?+
Usually yes once running, but expect hard cold starts and rough warm-up. Repair it before cold weather to avoid no-starts.
Can I just clear P0678?+
It returns on the next cold start until the failed glow plug or open circuit is repaired. Clearing only resets the light.
Related codes
Often seen with P0678
Read & clear P0678 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