P0674Powertrain
Powertrain · SAE
Glow Plug Cylinder 4 Circuit — Malfunction
Meaning
The ECM or GCU has detected a fault in the glow plug circuit for cylinder 4. The glow plug does not reach the required preheat temperature due to an electrical anomaly in its supply circuit.
Common causes
- Cylinder 4 glow plug short circuit or open circuit (burned-out heating element)
- Glow plug resistance out of specification (wear or internal fracture)
- Damaged or corroded wiring/connector for cylinder 4 glow plug
- Faulty GCU output driver for cylinder 4
- Short to ground in the glow plug circuit
- Broken glow plug ground connection
Symptoms
- Malfunction indicator lamp (MIL) illuminated
- Hard cold start, especially at cylinder 4
- White or grey exhaust smoke at startup
- Rough idle after cold start
- Sometimes no obvious symptoms if other glow plugs compensate
Severity
Moderate: a single faulty glow plug reduces preheat efficiency; at very low temperatures it can prevent starting and cause premature wear from incomplete combustion.
What to do
- Measure cylinder 4 glow plug resistance with connector unplugged (typical 0.5–2 Ω)
- Check supply voltage at the glow plug during the preheat cycle
- Inspect glow plug wiring and connector for damage or corrosion
- Replace cylinder 4 glow plug if resistance is out of specification or element is open
- Check the GCU module if the fault persists after glow plug replacement