P0684moderate severityPowertrain
Glow Plug Control Module to PCM Communication Circuit Range/Performance
on 2000 BMW 528i 2.8L I6 M52 · RWD
What this code means
The PCM detects an out-of-range or implausible signal in communication with the glow plug control module. Glow plug timing and operation may be incorrect.
Symptoms
- Difficult cold starting
- Glow plug light flashing
- White exhaust smoke when cold
Common causes
- Damaged communication wiring
- Poor connector contact
- Faulty glow plug control module
- PCM software fault
Diagnostic steps
- Retrieve related fault codes
- Inspect and test communication wiring
- Check for correct reference voltage
- Test or replace glow plug module
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