Diesel Trouble Codes

P0670 — Glow Plug Control Module Circuit (L5P Duramax)

Diagnostic reference for P0670 on L5P Duramax (2017–present).

Updated September 2, 2026

What it means

The PCM has detected a fault in the glow-plug control module circuit. On L5P Duramax, cold start uses glow plugs (8) + glow plug control module; NOT a grid heater.1

Most likely causes

  1. Glow plug control module internal fault or power/ground loss — Module not responding or power/ground circuit open/short; PCM sets P0670 for control-module circuit fault.1
  2. Wiring harness chafing / connector corrosion at glow plug control module — Open/short in module harness triggers control-module circuit DTC.1
  3. Repeated individual glow plug failures stressing the control module — L5P glow plug failures are reported; repeated failures can lead to module circuit faults.2

How to diagnose

  1. Verify freeze frame and confirm P0670 is present with glow-plug system active (cold start conditions).
  2. Inspect glow plug control module connectors for corrosion, bent pins, and harness chafing; check module power and ground circuits for continuity and proper voltage.
  3. Command glow plug system with scan tool and monitor module communication/status; look for module response failure indicating internal fault.
  4. Check related glow plug circuit codes (e.g., P0380, P067x, P128C) to identify if individual plug faults are contributing.
  5. If module tests good, inspect individual glow plug circuits for high resistance/short that may overload module; document findings before replacement.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by region and shop; obtain local estimate.

When to see a pro

If diagnosis points to glow plug control module replacement or internal harness repair, have a qualified diesel technician perform the work. Glow plug service on high-compression diesel requires proper torque and electrical safety practices.

Sources

  1. Curated DTC seed — L5P Duramax (curated) ↩︎ ↩︎ ↩︎

  2. NHTSA owner report 11718543 ↩︎

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