P0678Powertrain
Powertrain · SAE
Glow Plug Cylinder 8 — Circuit
Meaning
The control module has detected an electrical fault in the glow plug circuit for cylinder 8. The glow plug may be open or shorted, or the wiring or control module may have a fault.
Common causes
- Cylinder 8 glow plug open or shorted to ground
- Damaged or oxidised connector or wiring to the glow plug
- Defective glow plug relay or glow plug control module (GSC)
- Glow plug worn out due to overheating or high mileage
- Interrupted supply voltage or ground in the control circuit
Symptoms
- Check engine light on
- Hard cold start
- Rough combustion at cylinder 8 during warm-up
- White or grey smoke on first start-up
- Possible engine shudder in the initial phase
Severity
Moderate: normal operation is possible in mild temperatures, but severe cold can make starting very difficult and prolong thermal stress on the cylinder.
What to do
- Measure glow plug resistance at cylinder 8 (typical 0.5–4 Ω); replace if out of specification
- Inspect connector and wiring for oxidation or breaks
- Check supply voltage at the GSC module
- Perform a functional test of the glow plug module using a scan tool
- Replace the GSC module if the circuit is not commanded despite intact wiring