Diesel Trouble Codes

P0380 — Glow Plug/Heater Circuit Malfunction — L5P Duramax

Diagnostic reference for P0380 on L5P Duramax (2017–present).

Updated October 15, 2026

What it means

The engine control module has detected an electrical fault in the glow plug heater circuit. On L5P 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.3
  2. Individual glow plug failure / open or shorted heater element — NHTSA reports of L5P Duramax with DTC P133X (Cylinder X Glow Plug Failure) leading to glow plug replacement and reprogramming; repeat failures on different cylinders observed.4
  3. High resistance / abnormal voltage in a cylinder glow plug control circuit — ECM detects abnormally high voltage or resistance in the control circuit for a cylinder glow plug.5

How to diagnose

  1. Verify code and freeze frame; confirm P0380 is present and check for companion codes P0670 or cylinder-specific glow plug codes.
  2. Inspect glow plug control module power/ground and harness for corrosion, chafing, or moisture; check module connectors for terminal damage.
  3. Perform electrical tests of glow plug control module circuit per service information; do not replace high-pressure fuel components for this code.
  4. Test individual glow plug resistance and control circuit continuity; compare to specification and identify open/shorted plugs.
  5. Clear codes, command glow plug activation with scan tool, and monitor circuit feedback for recurrence.

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 service on L5P involves high-current circuits and ECM calibration; improper testing can damage the control module. Have diagnosis confirmed by a qualified diesel technician. Do not attempt high-pressure fuel system service for this code.

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 — L5P Duramax (curated) ↩︎

  2. Curated DTC seed — L5P Duramax (curated) ↩︎

  3. Curated DTC seed — L5P Duramax (curated) ↩︎

  4. NHTSA owner report 11718543 ↩︎

  5. Curated DTC seed — L5P Duramax (curated) ↩︎

Repair videos: P0380 on the L5P Duramax

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

How to change a glow plug on a L5P DURAMAX + test drive — Bought2Build · 48K views

Replacing Bad Glow Plug on L5P Duramax — C Farmer · 18K views

Replacing glow plugs on 2018 GMC Duramax 6.6 Liter diesel driver's side Pt 1 — Daryl Sparks - Sparks Automotive · 34K views