Error code

OBD2 P0678

OBD2P0678
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Cylinder 8 Glow Plug Circuit.

Severity

moderateCan drive, but may experience difficulty starting and reduced performance during cold weather.

Summary

P0678 indicates a malfunction in the glow plug circuit for cylinder 8 of a diesel engine, preventing proper operation during cold starts.

Symptoms

  • Long crank times
  • Lower power during engine warmup
  • Difficulty starting when cold
  • Check engine light on
  • Longer than normal glow plug activation time

Common Causes

  • Wiring damage or poor connection
  • Faulty relay
  • Glow plug control module failure
  • Defective glow plug
  • Engine Control Module (ECM) issue

Diagnosis

  1. Identify cylinder 8 location based on vehicle manufacturer specifications.
  2. Check wiring diagram for glow plug circuit in cylinder 8.
  3. Inspect wiring for damage or corrosion.
  4. Test relay operation and voltage presence.
  5. Swap glow plug with another cylinder's to isolate the issue.
  6. Verify controller output signal if timer is specific to cylinder.

Fixes

  • Replace faulty glow plug, relay, control module, or wiring as needed.

FAQ

What should I do before replacing the glow plug?

Ensure you diagnose the entire system to confirm that the issue is not with the wiring, relays, or control module.

Can I drive my car if P0678 appears?

Yes, but expect difficulty starting and reduced performance during cold weather until the issue is resolved.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

More OBD2 codes

All OBD2 codes →Search more codes →