P0380 — Glow Plug/Heater Circuit Malfunction (L5P Duramax)

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

Updated September 2, 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, e.g., P128C for cylinder 1.⁵

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.

Parts and tools you may need

• Digital multimeter
• Scan tool with bi-directional control
• Glow plug test light / breakout box
• Service information wiring diagrams

Rough cost and difficulty

Parts and labor vary by region and shop; glow plug replacement often requires intake removal on L5P and may include module reprogramming.

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.

Sources