P066F–P069D Cylinder 3 Glow Plug Control Circuit High
The voltage on this circuit is sitting near battery voltage. Typically a short to a positive feed, or a disconnected sensor floating high.
Can you drive it? Glow plugs only help a cold diesel start. Once the engine is running it normally drives as usual, but cold starts get harder and smokier until it is fixed.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P066F | Cylinder 3 Glow Plug Control Circuit High | Investigate soon |
P067B | Cylinder 4 Glow Plug Control Circuit High | Investigate soon |
P067D | Cylinder 5 Glow Plug Control Circuit High | Investigate soon |
P069B | Cylinder 9 Glow Plug Control Circuit High | Investigate soon |
P069D | Cylinder 10 Glow Plug Control Circuit High | Investigate soon |
The definition
P066F: Cylinder 3 Glow Plug Control Circuit High.
P066F is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Unplug the sensor and check whether the signal falls. If it stays high, suspect the wiring rather than the sensor.
- Check the earth path - a missing earth makes a sensor read high.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads your engine ECU's fault codes and the live measuring blocks behind them, and clears the codes once you have fixed the fault. On the engine it also does what a generic OBD reader cannot on a VAG: coding, adaptations, and Stage 1–3 flashing on Bosch ME7 petrol ECUs, with a backup saved every time it reads your ECU.
$249 once. No subscription, unlimited cars. Windows 10/11.
See VAGPULSE — $249 Look up another codeSoftware downloads instantly · cable in stock, ships in 3 business days · cable guarantee — refund if it won't connect
Prefer to work on your phone? The VAGPULSE Android app is a free download and its demo mode runs against a sample car with no hardware at all, so you can see exactly what it reads before spending anything. Reading your car with it needs the VAGPULSE cable, which comes with the licence.
Common questions
What does P066F mean?
P066F means Cylinder 3 Glow Plug Control Circuit High. The voltage on this circuit is sitting near battery voltage. Typically a short to a positive feed, or a disconnected sensor floating high.
Can I drive with P066F?
Glow plugs only help a cold diesel start. Once the engine is running it normally drives as usual, but cold starts get harder and smokier until it is fixed.