Diesel Trouble Codes

P0380 — Glow Plug/Heater Circuit Malfunction (LLY / LBZ / LMM Duramax)

Diagnostic reference for LLY/LBZ/LMM Duramax 2004.5–2010.

Updated September 2, 2026

What it means

The engine control module has detected an electrical fault in the glow plug heater circuit. On LLY/LBZ/LMM Duramax the cold-start system uses 8 glow plugs plus a glow plug control module; there is no grid heater.12

Most likely causes

  1. Glow plug control module circuit fault / module failure — PCM detects a fault in the glow-plug control module circuit, often due to a failed control module, wiring/connector corrosion, or a short/open in the glow plug harness. P0670 is the companion code for the control module circuit on this platform.2
  2. Open or short in individual glow plug circuit — An open or short in one or more of the eight glow plug circuits can trigger a generic heater circuit malfunction. The platform uses eight glow plugs with a dedicated control module and no grid heater.12
  3. Wiring/connector corrosion or high resistance at glow plug harness — Corrosion or damaged connectors in the glow plug harness can cause the ECM to see an out-of-range heater circuit condition.2

How to diagnose

  1. Verify code P0380 is present and check for related glow-plug codes such as P0670 or P067x.
  2. Inspect glow plug control module power/ground and signal circuits for opens/shorts/corrosion per platform wiring.
  3. Check glow plug harness connectors for corrosion, moisture, or damage; verify continuity to each glow plug.
  4. Use a scan tool to view glow plug control module data and commanded on-time; compare to expected values for LLY/LBZ/LMM cold-start strategy.
  5. If a specific cylinder glow plug code is present, isolate that circuit; otherwise treat as a general heater circuit fault.

Parts and tools you may need

Rough cost and difficulty

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

When to see a pro

Glow plug and high-current circuits can cause thermal events. Have a qualified diesel technician confirm diagnosis before replacing components. Do not perform step-by-step repair of safety-critical systems. If cold-start performance is degraded, seek professional service promptly.

Sources

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

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