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…
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
- 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
- Open or short in glow plug wiring/harness — An electrical fault in the glow plug heater circuit as detected by the ECM.1
- 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
- Verify code and freeze frame; confirm cold-start symptoms.
- Inspect GPCM power/ground and signal circuits; check for corrosion or damage.
- Test glow plug resistance and continuity to the GPCM; look for opens/shorts in the harness.
- Check GPCM operation and communication per service information; evaluate replacement if circuit fault persists.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| Battery and charging voltage | 12.6–12.7 V at rest when fully charged; about 13.5 V running | Engine off, then running with loads on | DieselHub |
| Glow plug resistance | Low — usually no more than about 6 Ω — and similar on every plug; an open reading means a failed plug | Engine off, meter lead to engine ground | DENSO |
Common mistake to avoid
Replacing glow plugs or the glow module before checking the batteries. The glow system draws heavily, and low battery voltage causes circuit faults that no part swap will fix. Source: FleetRabbit — P0670 glow plug control module fault.
Parts and tools you may need
- Digital multimeter
- Glow plug test light
- Wiring diagram for LB7 GPCM circuit
- Replacement glow plugs (as needed)
- Glow plug control module
Tools you’ll need
- digital multimeter — Measures glow plug resistance and checks for opens/shorts in the GPCM wiring harness.
- OBD-II scan tool — Reads P0380 and freeze frame data to confirm cold-start conditions and monitor GPCM-related parameters.
- test light — Quickly verifies power and ground presence at the GPCM and individual glow plug circuits.
- wiring diagram — Identifies correct GPCM power, ground, and signal circuits for targeted inspection and testing.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| Glow plugs (full set) | $80–$250 | 2–6 hrs | DIY with tools and a manual |
| Glow plug relay or control module | $60–$400 | 0.5–2 hrs | Easy DIY |
Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.
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.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
Spotted an error, or something missing? Tell us
Run a LB7 Duramax? This goes straight to the editor — it is not published.