P066A–P069C Cylinder 1 Glow Plug Control Circuit Low
The voltage on this circuit is sitting near zero. Typically a short to earth, or a sensor that has failed to its low end.
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 |
|---|---|---|
P066A | Cylinder 1 Glow Plug Control Circuit Low | Investigate soon |
P066C | Cylinder 2 Glow Plug Control Circuit Low | Investigate soon |
P067A | Cylinder 4 Glow Plug Control Circuit Low | Investigate soon |
P067C | Cylinder 5 Glow Plug Control Circuit Low | Investigate soon |
P067E | Cylinder 6 Glow Plug Control Circuit Low | Investigate soon |
P068E | Cylinder 8 Glow Plug Control Circuit Low | Investigate soon |
P069A | Cylinder 9 Glow Plug Control Circuit Low | Investigate soon |
P069C | Cylinder 10 Glow Plug Control Circuit Low | Investigate soon |
The definition
P066A: Cylinder 1 Glow Plug Control Circuit Low.
P066A 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. If the reading jumps to full scale, the wiring is fine and the sensor has failed low.
- Check the sensor's 5V supply and its earth before condemning the sensor itself.
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.
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Common questions
What does P066A mean?
P066A means Cylinder 1 Glow Plug Control Circuit Low. The voltage on this circuit is sitting near zero. Typically a short to earth, or a sensor that has failed to its low end.
Can I drive with P066A?
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.