Common Signs
- 🚩 Hard starting (especially in cold/damp weather),
- ⚠️ Engine shaking or stalling at idle,
- ⚡ Combustion issues (misfires),
- 💡 Engine fault light (ESP/Check Engine) illuminated,
- 📉 Increased fuel consumption.
Probable Causes
- Faulty glow plug (cylinder 3): Internal failure or resistance out of specification.
- Electrical issue:
- Damaged/oxidized/short-circuited wires (between the module and glow plug #3),
- Loose or corroded connectors.
- Control module failure (GPCM): Malfunction in the circuit managing cylinder 3.
- Failed glow plug relay: Unable to power the circuit.
- Blown fuse: In the glow plug power circuit.
Recommended Diagnosis
- Check glow plug #3 resistance (typical value: 0.1–2 Ω). Infinite resistance = faulty plug.
- Visually inspect wiring: Look for burns, cuts, or corrosion on cylinder 3’s circuit.
- Test power supply: Use a multimeter to check voltage at the glow plug terminals during startup.
- Check relay and fuses: Ensure they are functioning properly.
- Scan the GPCM module: Look for other related fault codes (e.g., P138A, P138B, P138D).
⚠️ Important: A faulty glow plug can damage the control module. Always test both!
Repair
- Replace glow plug #3 (average cost: €20–80 per unit),
- Repair damaged wires/connectors,
- Replace GPCM module or relay if faulty.
Good to Know
- Repeated forced starting with a faulty glow plug can damage the engine (premature wear, fouling).
- After repair, reset the engine computer to turn off the warning light.
If you don’t have the necessary equipment, consult a specialized diesel mechanic! 🔧