P066C
Cylinder 2 Glow Plug Control Circuit Low
Diesel glow plug / preheat
Generic OBD-II
High
What it means
P066C is a diesel code: the glow plug control module has detected an abnormally low voltage on the control circuit for the cylinder 2 glow plug. Glow plugs preheat the combustion chamber for cold starts, so a fault here mainly shows up as hard cold starting, rough warm-up, and cold-start smoke rather than a breakdown.
High
Can I keep driving? Usually yes, but expect hard cold starts and rough cold running until the cylinder 2 glow plug circuit is fixed.
Common symptoms
What you'll notice
- Hard starting, especially in cold weather
- Rough running or a light 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 2 glow plug (open or shorted element)Likely
- Open, shorted, or chafed wiring in the glow plug control circuitCommon
- Poor or corroded connection at the glow plug or module connectorCommon
- Faulty glow plug control module driving the circuit lowLess often
How to diagnose & fix
Work through it in order
- Scan and read freeze-frame to confirm the fault is on cylinder 2's control circuit.
- Inspect the wiring and connector from the glow plug module to the cylinder 2 glow plug for damage or corrosion.
- Measure the glow plug's resistance and replace it if it is open or out of spec.
- Check the glow plug control module and its grounds, then clear and re-test on a cold start.
FAQ
Quick answers
Is it safe to drive with P066C?+
Generally yes in warm weather. A single weak glow plug mostly shows up as hard cold starting and rough warm-up, not a breakdown, but fix it before cold weather.
Can I just clear P066C?+
You can, but it returns once the engine is cold again if the glow plug or its circuit is still faulty.
Related codes
Often seen with P066C
Read & clear P066C 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