P0380
Glow Plug/Heater Circuit A.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 3
- AreaIgnition system or misfire
- 80
- FaultThe specific fault in that area
What it means
P0380 is the SAE J2012 generic code for a fault in glow plug or heater circuit 'A', most often found on diesel engines. The engine control unit (or a separate glow plug control module) monitors the circuit and has seen a voltage, current or feedback signal outside the expected range. Which plugs or wiring make up circuit 'A' depends on the model and engine.
Symptoms
- Glow plug warning light on or flashing
- Hard starting when cold, especially in cold weather
- Extra white or grey smoke and rough running just after a cold start
- Engine misfiring or running unevenly until warmed up
- Slightly higher fuel consumption or noisy idle when cold
- Engine management light on
Possible causes
- One or more failed glow plugs (open circuit or high resistance)likely
- Damaged, corroded or loose wiring, connectors or earth connections in the glow plug circuitlikely
- Faulty or corroded glow plug supply or feed wiring, or a blown fuse or fusible linkpossible
- Faulty glow plug relay or control modulepossible
- Low battery voltage or poor charging causing the circuit to read out of rangepossible
- Software fault in the control unit where the manufacturer has issued an updated calibrationrare
How to diagnose
- Read all stored and pending codes and note the freeze frame data, including coolant and ambient temperature, and check for related codes for other glow plug circuits or the control module.
- Check battery condition and charging voltage, as low voltage can set glow plug faults.
- Visually inspect the glow plug wiring, connectors, fuses and earth points for damage, heat, corrosion or looseness.
- Check the relevant fuse and fusible link, and confirm the circuit has supply and earth when glow plugs are commanded on.
- Measure the resistance of each glow plug against the manufacturer's specification, with the wiring disconnected.
- Measure current draw or voltage drop in the circuit during the glow cycle, following the manufacturer's procedure.
- Use a scan tool to command the glow plug system and check that the relay or control module responds. The method depends on the model.
- Check for manufacturer service bulletins and calibration updates for your engine.
How to fix
- Replace any failed glow plugs, ideally the full set if they are old, using the correct type for the engine.
- Repair or replace damaged wiring, connectors or earth connections.
- Replace blown fuses only after finding and fixing the cause of the overload.
- Replace a faulty glow plug relay or control module, then carry out any required coding or adaptation for the model.
- Restore battery and charging system health if voltage is low.
- Apply an updated control unit calibration only if the manufacturer lists it as a fix for this fault.
Can I keep driving?
Medium severity
The car can usually be driven, but cold starting may be difficult and smoky, and the fault may worsen. Book it in soon, and avoid repeated long cranking attempts, which strain the battery and starter.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.