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StartingSeverity Medium: diagnose soon

P0684Glow Plug Control Module to PCM Communication Circuit Range/Performance

What it means

The feedback signal from the glow plug module is implausible.

Symptoms

  • Hard cold start
  • Glow plug lamp on

Common causes

  • Faulty glow plug module
  • Intermittent wiring
  • Failed glow plugs

What to check first

  1. Measure all glow plugs
  2. Check the feedback wiring
  3. Replace the module only after the plugs and wiring check out
Can I drive with P0684? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

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P0684: questions and answers

What does P0684 mean?

P0684: Glow Plug Control Module to PCM Communication Circuit Range/Performance. The feedback signal from the glow plug module is implausible.

What are the symptoms of P0684?

Hard cold start. Glow plug lamp on.

What causes P0684?

Faulty glow plug module. Intermittent wiring. Failed glow plugs.

How do you diagnose P0684?

1. Measure all glow plugs 2. Check the feedback wiring 3. Replace the module only after the plugs and wiring check out

Can I drive with P0684?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.