P066F
Cylinder 3 Glow Plug Control Circuit High.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 6
- AreaComputer and output circuits
- 6F
- FaultThe specific fault in that area
What it means
P066F is the generic code for a high signal in the cylinder 3 glow plug control circuit. The engine control unit or glow plug control module monitors the voltage or feedback on that circuit and saw it higher than expected, which can mean a short to voltage or a fault in the driver. It applies to diesel engines, and the exact circuit layout depends on the model and engine.
Symptoms
- Engine management or glow plug warning light on
- Hard starting or extended cranking on cold mornings
- White smoke and rough running just after a cold start
- Misfire or uneven idle until the engine warms up
- Slightly higher fuel use or noisy cold running
Possible causes
- Faulty cylinder 3 glow plug with internal short or incorrect resistancelikely
- Damaged, chafed or corroded wiring or connector on the cylinder 3 glow plug feed or control circuit, including a short to voltagelikely
- Faulty glow plug control module with a failed output driver for cylinder 3possible
- Poor earth or voltage supply fault affecting the glow plug systempossible
- Loose or corroded glow plug terminal or connection at the plugpossible
- Outdated or faulty control unit software, only where the manufacturer has a known faultrare
How to diagnose
- Read all stored and pending codes and note any other glow plug codes, then review freeze frame data for engine temperature and battery voltage.
- Check battery condition and charging voltage, as low or unstable voltage can upset glow plug diagnostics.
- Visually inspect the glow plug wiring, connectors and terminals on cylinder 3 for heat damage, chafing, corrosion or looseness.
- Check the relevant fuses and relays for the glow plug system against the manufacturer wiring diagram.
- Measure the resistance of the cylinder 3 glow plug against the manufacturer specification, and compare it with the other plugs.
- Check the control circuit for a short to voltage and for a good earth using the wiring diagram, with the module disconnected where specified.
- Use a scan tool with live data or actuator tests, if supported, to see how the module commands and reads cylinder 3.
- If the wiring and plug are sound, check for a known software update or module fault for that model before replacing the module.
How to fix
- Replace the faulty cylinder 3 glow plug, using the correct specification part and torque.
- Repair or replace damaged wiring, connectors or terminals on the cylinder 3 circuit.
- Clean or repair poor earth and power supply connections.
- Replace the glow plug control module if its output is confirmed faulty.
- Apply a manufacturer calibration update only where an outdated or faulty calibration is a known cause for that model.
Can I keep driving?
Medium severity
The car can usually be driven short term, but cold starting may get worse and a short circuit could damage the module or wiring. Get it checked soon, particularly before cold weather.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.