P068F
Cylinder 8 Glow Plug Control Circuit High.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 6
- AreaComputer and output circuits
- 8F
- FaultThe specific fault in that area
What it means
P068F means the engine or glow plug control module detected a higher than expected voltage on the control circuit for the cylinder 8 glow plug. It applies to diesel engines with at least eight cylinders and individually controlled glow plugs. The module compares the commanded state of the circuit with the actual voltage or feedback, and sets the code when the circuit reads high, for example from a short to voltage or a driver fault.
Symptoms
- Malfunction indicator lamp or glow plug warning lamp on
- Harder cold starting, especially in cold weather
- White smoke or rough running for the first minute after a cold start
- Slightly increased cold-start emissions and noise (diesel knock)
- Reduced cold-start performance or the engine entering a reduced-output mode on some models
Possible causes
- Cylinder 8 glow plug control wire shorted to a voltage supply or to another live circuitlikely
- Damaged, corroded or loose connector or terminal at the cylinder 8 glow plug or at the control modulelikely
- Faulty cylinder 8 glow plug (internal short or incorrect resistance)possible
- Faulty glow plug control module or its output driver for cylinder 8possible
- Wiring harness chafed or heat-damaged near the cylinder head or exhaustpossible
- Fault in the engine control unit or outdated software, where the manufacturer has published a known issue for that enginerare
How to diagnose
- Read all stored and pending codes and the freeze frame data. Note engine temperature, battery voltage and whether other glow plug codes are present.
- Check the battery condition and charging voltage, since low or unstable voltage can cause misleading glow plug circuit faults.
- Visually inspect the glow plug wiring, connectors and the control module connector for corrosion, water ingress, heat damage and chafing, especially around cylinder 8.
- Check for any technical service bulletins or known issues for the specific engine and model, as the glow plug circuit layout varies by manufacturer.
- With the circuit unplugged, measure the cylinder 8 control wire for unwanted voltage, and check for shorts to supply or to adjacent wires using the wiring diagram for that vehicle.
- Measure the cylinder 8 glow plug resistance and compare it with the manufacturer's specification, and compare it with the other glow plugs.
- Use a bi-directional scan function, if available, to activate the glow plugs and monitor the circuit response and current draw.
- If the wiring and glow plug are good, test the control module power, earth and output signals before condemning the module.
How to fix
- Repair or replace the damaged wiring section causing the short to voltage, and secure the harness away from heat and sharp edges.
- Clean, repair or replace corroded or damaged connectors and terminals.
- Replace the cylinder 8 glow plug if it is out of specification, following the correct torque procedure to avoid breaking it.
- Replace the glow plug control module if its output is confirmed faulty.
- Apply the manufacturer's updated control unit software only if a known issue for this fault is documented, then clear the codes and retest.
Can I keep driving?
The car can usually be driven, as glow plugs mainly matter for cold starting. Book it in soon, particularly before cold weather, as starting may become difficult and other glow plug faults may develop.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.