Diesel Trouble Codes

P0380 — Glow Plug/Heater Circuit Malfunction (LB7 Duramax)

P0380 on the LB7 Duramax means the ECM has detected an electrical fault in the glow plug heater circuit. The LB7 uses eight glow plugs controlled by a glow…

Updated September 2, 2026

What it means

The ECM has detected an electrical fault in the glow plug heater circuit. On the LB7 Duramax this is a valid glow plug/heater circuit malfunction code; the engine uses glow plugs with a GPCM for cold start.1

Most likely causes

  1. Glow plug control module (GPCM) circuit fault — The PCM has detected a fault in the glow-plug control module circuit, which can set P0380 in addition to P0670.2
  2. Open or short in glow plug wiring/harness — An electrical fault in the glow plug heater circuit as detected by the ECM.1
  3. Failed glow plug(s) — A failed glow plug can cause the heater circuit to read out of range, triggering the ECM electrical fault detection.1

How to diagnose

  1. Verify code and freeze frame; confirm cold-start symptoms.
  2. Inspect GPCM power/ground and signal circuits; check for corrosion or damage.
  3. Test glow plug resistance and continuity to the GPCM; look for opens/shorts in the harness.
  4. Check GPCM operation and communication per service information; evaluate replacement if circuit fault persists.

Parts and tools you may need

Rough cost and difficulty

Parts cost varies by component; labor depends on access and testing time.

When to see a pro

If hard starting persists, multiple glow plug codes appear, or wiring faults are found in the engine harness, have a qualified diesel technician diagnose and repair. Do not attempt high-pressure fuel system service. If the vehicle is unsafe to drive, tow it.

Sources

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

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