P066B

Symptoms

• Difficulty starting a diesel engine at low temperatures
• The Check Engine light comes on
• Extended warm-up time before starting
• White smoke from the exhaust pipe during cold start
• Unstable engine operation at idle after starting

Causes

• Short circuit of the control wire to the power line (+12 V)
• Open ground circuit in the glow plug control circuit
• Glow Plug Control Module (GPCM) Malfunction
• Damage to control circuit wiring or connectors
• Internal ECU fault

How to Fix

1. Read error codes with an OBD-II scanner and capture a freeze frame of the data
2. Inspect the wiring and connectors of the cylinder 1 glow plug and GPCM
3. Measure the voltage in the spark plug control circuit (the standard corresponds to the manufacturer's specifications)
4. Check the ground circuit for open circuit with a multimeter
5. Check signal wire for short circuit to power
6. If the wiring is working properly, diagnose and replace the GPCM or ECU

Related codes

Error P066B by Vehicle Brand