P068D
Cylinder 7 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
- 8D
- FaultThe specific fault in that area
What it means
P068D means the engine or glow plug control module has detected a high voltage condition on the control circuit for the cylinder 7 glow plug. The unit compares the commanded state of the glow plug driver with the voltage it measures on that circuit. When the reading is higher than expected, it sets the code. Cylinder 7 implies an engine with at least seven cylinders, and how the circuit is arranged depends on the model and engine.
Symptoms
- Glow plug warning light on, or engine management light on
- Harder or longer cold starting, especially in cold weather
- White smoke and rough running for the first minutes after a cold start
- Slightly increased cold-start emissions or a noticeable diesel smell
- Other glow plug circuit codes stored alongside it
- No noticeable symptoms on a warm engine
Possible causes
- Wiring fault on the cylinder 7 glow plug control circuit, such as a short to voltage or chafed insulationlikely
- Corroded, loose or damaged connector at the cylinder 7 glow plug or at the control modulelikely
- Failed or shorted cylinder 7 glow plugpossible
- Faulty glow plug control module or driver output stagepossible
- Low or unstable supply voltage from a weak battery or poor earth connection affecting the circuit readingpossible
- Outdated or faulty control unit software, where the manufacturer has issued a correction for this faultrare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting engine temperature, battery voltage and whether other glow plug codes are present.
- Check battery condition and charging voltage, and inspect the main earth connections, as low voltage can upset circuit monitoring.
- Visually inspect the glow plug wiring and connectors for cylinder 7, looking for chafing, heat damage, corrosion, water ingress and bent or pushed-back pins.
- Check the glow plug and module for any manufacturer service information specific to your model and engine, as the circuit layout varies.
- With the ignition off and the module disconnected, test the cylinder 7 control wire for continuity and for any short to voltage or earth, following the wiring diagram.
- Measure the cylinder 7 glow plug resistance and compare it with the specification for the engine.
- Use a scan tool to activate the glow plugs, if supported, and check the commanded and actual output for cylinder 7 against the other cylinders.
- Check whether a software update is listed for the control unit and relevant to this fault.
How to fix
- Repair or replace the damaged wiring section on the cylinder 7 control circuit, and secure it clear of heat and abrasion.
- Clean, repair or replace the corroded or damaged connectors and terminals.
- Replace the cylinder 7 glow plug if it is out of specification, following the correct torque and removal procedure for the engine.
- Replace the glow plug control module if the circuit and plug are proven sound and the module output is faulty.
- Replace a weak battery or repair poor earth connections, then clear the codes and confirm the fault does not return.
- Update the control unit software only where the manufacturer lists an update for this fault.
Can I keep driving?
The car can usually be driven short term, as the engine will normally run once warm, but cold starts may become difficult. Get it checked soon, as a short to voltage could damage the control module or lead to further glow plug faults.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.