Diesel Trouble Codes

P0670 — Glow Plug Control Module Circuit (LB7 Duramax)

The PCM has detected a fault in the glow-plug control module circuit on the LB7 Duramax. This is a cold-start system fault; the Duramax uses glow plugs with a…

Updated September 2, 2026

What it means

The engine control module has detected an electrical fault in the glow-plug control module circuit. On the LB7 Duramax, cold start uses eight glow plugs controlled by a glow plug control module (GPCM).1

Most likely causes

  1. Glow plug control module (GPCM) internal failure or power/ground loss — The PCM monitors the GPCM control circuit; loss of power, ground, or internal module failure sets P0670.1
  2. Open or short in GPCM harness/connectors — Chafed or corroded wiring to the GPCM can cause the PCM to see an out-of-range circuit condition.1
  3. Related glow-plug heater circuit malfunction — A broader glow-plug/heater circuit fault such as P0380 can accompany or contribute to a GPCM circuit fault on this platform.2

How to diagnose

  1. Verify freeze frame and confirm P0670 is present with cold-start symptoms.
  2. Inspect GPCM power and ground feeds and connector for corrosion, moisture, or damage.
  3. Check GPCM harness for opens/shorts to ground or battery; compare to wiring diagram.
  4. Command GPCM activation with a scan tool and monitor GPCM feedback/state PID if available.
  5. Inspect glow plug supply wiring and individual glow plug resistance for shorts/opens that may load the GPCM circuit.
  6. Clear codes, cold soak, and retest for P0670 return.

Parts and tools you may need

Rough cost and difficulty

Parts cost varies by supplier and region; labor depends on access and diagnostic time. Obtain local quotes.

When to see a pro

If wiring faults are found in high-current glow-plug circuits, or if GPCM replacement is required, have a qualified diesel technician perform the work to avoid electrical damage or incorrect cold-start operation. Safety-critical high-current circuits should not be serviced without proper training and tools.

Sources

  1. Curated DTC seed — LB7 Duramax (curated) ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — LB7 Duramax (curated) ↩︎

Watch a repair

Third-party videos, not ours — for illustration. Confirm anything against the factory service information for your truck.

How to Replace Glow Plug Control Module 2008-2010 Ford F-250 — TRQ · 19K views

How to Fix P0670 Engine Code in 3 Minutes [2 DIY Methods / Only $9.74] — nonda · 73K views