Diesel Trouble Codes

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

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

Updated October 15, 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.

Specs and test values

CheckNormal readingWhen to measureSource
Battery and charging voltage12.6–12.7 V at rest when fully charged; about 13.5 V runningEngine off, then running with loads onDieselHub
Glow plug resistanceLow — usually no more than about 6 Ω — and similar on every plug; an open reading means a failed plugEngine off, meter lead to engine groundDENSO

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

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
Glow plugs (full set)$80–$2502–6 hrsDIY with tools and a manual
Glow plug relay or control module$60–$4000.5–2 hrsEasy 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

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.

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

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

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

Repair videos: P0380 on the LLY-LMM Duramax

Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.

How To EASILY Test and Fix Glow Plugs in a 2006 Duramax! — Snow Family Racing · 15K views

Diagnose Glow Plug 6.6 Duramax-Angry Mechanic P0671,P0672,P0673,P0674,P0675 P0676,P0677,P0678 — He Who Angers You · 306K views

How to Test and Replace a Duramax Glow Plug | P0678 Code Fix — Fix it John · 78K views