P0670Powertrain
Powertrain · SAE
Glow Plug Module Control Circuit — Malfunction
Meaning
The ECM has detected a fault in the control circuit of the Glow Plug Control Module (GCU). The control signal between the ECM and GCU is absent, interrupted, or out of range, making the preheating system uncontrollable by the engine management.
Common causes
- Internal GCU module failure
- Short circuit or open circuit in the ECM-to-GCU wiring harness
- Oxidized or loose GCU connector pins
- GCU supply voltage or ground out of specification
- Disturbed CAN/LIN communication signal between ECM and GCU
- ECM not generating the correct command signal to the GCU
Symptoms
- Glow plug system non-operational
- Glow plug indicator absent or abnormal
- Hard cold start
- Malfunction indicator lamp (MIL) illuminated
- Additional DTCs for individual glow plugs possible (P0671–P0676)
Severity
High: without a functioning GCU module, the entire preheating system is inoperative; the diesel engine cannot start correctly at low temperatures.
What to do
- Check GCU module supply voltage and ground connections
- Inspect wiring and connector between ECM and GCU
- Measure the communication line (CAN/LIN or PWM) between ECM and GCU with an oscilloscope
- Replace the GCU module if supply is correct but the module does not respond
- Reprogram or replace the ECM if the command signal is not generated correctly