OBD-II · Engine and powertrain (P)
P0684
Glow plug control module to engine computer communication range/performance
What it means
The glow plug control module is communicating with the engine computer, but the signal is implausible or erratic.
Symptoms
- harder starting when cold
- rough running and white smoke for the first moments after a cold start
- glow plug light may flash
- possibly no symptoms in warm weather
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | failing glow plug control module |
| 02 | high resistance or intermittent wiring |
| 03 | poor ground |
| 04 | glow plug faults reported in an unexpected way |
What to check, step by step
- 01Check module ground and supply under load.
- 02Inspect connectors and wiring for intermittent faults (wiggle test).
- 03Check all glow plugs.
- 04Replace the module if the fault persists with good wiring.