P066C

Cylinder 2 Glow Plug Control Circuit Low

Q: 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.

Q: 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.

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.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P066C yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX