P06C4
Cylinder 12 Glow Plug Circuit Range/Performance
Diesel glow plug / preheat
Generic OBD-II
High
What it means
P06C4 is a diesel-engine code showing the cylinder 12 glow plug circuit is operating outside its expected range, typically from a degraded glow plug or high-resistance wiring. Glow plugs preheat the cylinders for easy cold starting, so this fault shows up as hard cold starts and rough running until the engine warms. The engine still runs, but the cylinder 12 glow plug circuit needs attention.
High
Can I keep driving? The engine still runs, but on a diesel it may be hard to start and run rough when cold until the cylinder 12 glow plug circuit is repaired.
Common symptoms
What you'll notice
- Hard starting, especially in cold weather
- Check-engine (or glow plug) light on
- Rough running and shudder when the engine is cold
- White or grey smoke from the exhaust on a cold start
Common causes
Most likely first
- Cylinder 12 glow plug drawing out-of-range current (degraded plug)Likely
- High-resistance wiring or connector on the cylinder 12 circuitCommon
- Corroded or loose connector at the glow plugCommon
- Glow plug control module fault on the cylinder 12 outputLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for glow plug codes on other cylinders.
- Measure the resistance of the cylinder 12 glow plug and compare to the others.
- Inspect the wiring and connector to cylinder 12 for corrosion or high resistance.
- Replace the glow plug or repair the circuit, then clear and re-test on a cold start.
FAQ
Quick answers
Is it safe to drive with P06C4?+
Yes once running, but cold starts get harder and the engine runs rough until warm, so repair it soon.
Can I just clear P06C4?+
It will return until the cylinder 12 glow plug or its circuit is repaired.
Related codes
Often seen with P06C4
Read & clear P06C4 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