Diesel Trouble Codes

P0670 — Glow Plug Control Module Circuit (LLY / LBZ / LMM Duramax)

Diagnostic reference for LLY/LBZ/LMM Duramax (2004.5–2010) P0670. Rank causes most-likely first.

Updated September 2, 2026

What it means

The PCM has detected a fault in the glow-plug control module circuit. On LLY/LBZ/LMM Duramax 2004.5-2010, glow plugs (8) + glow plug control module are used for cold start; there is no grid heater. Code P0670 applies to this platform.12

Most likely causes

  1. Glow plug control module failure — The dedicated glow plug control module is malfunctioning or has internal electrical fault. Typical on LLY/LBZ/LMM Duramax 2004.5-2010 with 8 glow plugs and a dedicated control module and no grid heater.1
  2. Wiring/connector corrosion or damage to glow plug control module circuit — Corrosion, chafing, or loose connections in the harness/connectors to the glow plug control module cause an open/short detected by PCM. Typical presentation for P0670 on these engines is wiring/connector corrosion or a short/open in the glow plug harness.1
  3. Short or open in glow plug harness / individual glow plug circuit — A short or open in the glow plug harness or at a glow plug can pull the control module circuit out of range. P0670 is described as a glow plug control module circuit malfunction often due to a failed module, wiring/connector corrosion, or a short/open in the glow plug harness on LLY/LBZ/LMM.1

How to diagnose

  1. Verify code P0670 is present and check for accompanying P067x glow plug codes; confirm platform is LLY/LBZ/LMM Duramax 2004.5-2010 with glow plugs + control module and no grid heater.
  2. Inspect glow plug control module connectors and harness for corrosion, moisture, oil contamination, and chafing; check power/ground feeds to the module. Typical causes include wiring/connector corrosion.
  3. Perform resistance/continuity checks of the glow plug control module circuit wiring from PCM to module and module to glow plugs; look for opens/shorts. P0670 typically involves wiring/connector corrosion or short/open in glow plug harness.
  4. Test glow plug control module command/response with a scan tool during cold-start enable; verify module powers the glow plugs and reports status. Module failure is a typical cause on this platform.
  5. If module tests good, isolate glow plug harness sections and check individual glow plug circuits for shorts/opens to ground or power that could affect the control module circuit. Short/open in glow plug harness is a listed typical cause.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by region and shop; control module, harness repairs, and diagnostic time differ. No fixed pricing provided.

When to see a pro

If wiring faults are found in high-current glow plug circuits, or control module replacement is required, have a qualified diesel technician perform diagnosis and repair to avoid electrical damage or incorrect cold-start operation. Do not attempt step-by-step repair of safety-critical systems. This guide is diagnostic only.

Sources

  1. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — LLY / LBZ / LMM 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