P066F
Cylinder 3 Glow Plug Control Circuit High
Glow plug / diesel preheat
Generic OBD-II
Medium
What it means
P066F means the engine computer has detected high voltage — an open or high-resistance condition — in the control circuit for the cylinder 3 glow plug on a diesel engine. Glow plugs preheat the combustion chamber for starting, so a fault here mainly shows up as hard, rough, or smoky cold starts rather than a warm-running problem.
Medium
Can I keep driving? Usually yes — the engine still runs, but cold starts can be harder, rougher, and smokier until the cylinder 3 glow plug circuit is repaired.
Common symptoms
What you'll notice
- Hard starting, especially in cold weather
- Glow plug or check-engine light on
- Rough running and white smoke right after a cold start
- Slightly reduced power until the engine warms up
Common causes
Most likely first
- Open or high-resistance cylinder 3 glow plug (burned out)Likely
- Open or damaged wiring/connector in the cylinder 3 glow plug circuitCommon
- Corroded or loose glow plug connectionCommon
- Faulty glow plug control moduleLess often
How to diagnose & fix
Work through it in order
- Scan and confirm P066F, then read freeze-frame for the conditions it set under.
- Measure the cylinder 3 glow plug resistance; an open or very high reading means a failed plug.
- Inspect the glow plug wiring and connector for opens, corrosion, or looseness.
- Replace the cylinder 3 glow plug if it tests bad; repair the wiring otherwise.
- If the plug and wiring are good, check the glow plug control module and its supply.
FAQ
Quick answers
Is it safe to drive with P066F?+
Usually — a diesel runs on its other cylinders, but expect harder, smokier cold starts. Fix it before winter to keep starting reliable.
Can I just clear P066F?+
You can, but it returns once the ECM re-tests the glow plug circuit unless the open plug or wiring is repaired.
Related codes
Often seen with P066F
Read & clear P066F 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