P0380 Glow Plug/Heater Circuit A Malfunction

P0380 points to a glow plug or heater circuit A malfunction. It is common on diesel applications where cold-start heating is monitored by the control system.

Code details

Generic OBD-II · P0

System: Ignition / Misfire
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace all glow plugs automatically; controller, power supply, wiring, and individual plug faults need to be separated.

Symptoms of P0380

Rough idle, shaking, or a stumble under acceleration.
A flashing check-engine light during an active misfire.
Power loss and higher fuel consumption.

Common causes of P0380

Worn spark plugs, ignition coils, or plug wires.
Fuel-delivery problems — injectors, pressure, or a lean/rich mixture.
Vacuum leaks, low compression, or a mechanical fault in that cylinder.

Useful checks before replacing parts

Check glow plug relay or control module command, fuse links, power feed, ground path, and circuit current draw.
Test individual glow plugs and harness connections using service-information limits for resistance or current.
Review cold-start symptoms, battery condition, ambient temperature, and related cylinder-specific glow plug codes.

Related OBD-II codes

These nearby ignition / misfire entries can help compare wording and pin down the fault area.