P0380
PowertrainGlow Plug/Heater Circuit "A"
There's a fault in the glow plug control circuit on a diesel engine. Either the glow plugs themselves, the relay/module that powers them, or the wiring isn't behaving as expected.
ⓘ Information only. This page provides general educational information about fault code P0380. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0380 mean?
P0380 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Glow Plug/Heater Circuit "A".
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light
- • Glow plug warning light (the curly icon)
- • Hard or extended cold-starting, particularly in winter
- • White smoke on cold start (diesel that hasn't fully fired)
- • Rough running for the first 30-60 seconds after starting cold
Possible causes
Causes commonly associated with P0380, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. One or more glow plugs failed (open circuit). Modern diesels need all plugs working for the warm-up sequence
- 2. Glow plug relay or control module failed, by far the most common cause on Ford, BMW, Vauxhall, and many VAG diesels
- 3. Damaged wiring or corroded connectors, glow plug looms run hot and corrode over years
- 4. Blown fuse for the glow plug circuit
- 5. Faulty ECU output (rare)
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Test each glow plug individually for resistance. A healthy glow plug measures around 0.5-1 ohm, an open-circuit one reads infinity
- 2. Check the glow plug relay, listen for it clicking when ignition is turned to position II in cold weather. No click is a strong indicator of relay failure
- 3. Inspect wiring and connectors at each plug. Heat-damaged or corroded connectors are common
- 4. Check the relevant fuse in the engine bay fuse box
- 5. On some cars, the glow plug control module is integrated into the ECU; in those cases it's a workshop-level diagnosis
Common questions about P0380
Will the car still start with bad glow plugs in summer? +
Often yes, when the engine is warm or the ambient is mild. Glow plugs are critical when the engine is cold, particularly below 5°C. Cars regularly start fine in summer with one or more glow plugs failed, then become impossible to start come November.
Should I replace all the glow plugs at once? +
Strongly recommended. They're all the same age and the same heat-cycled history. If one's failed, the others aren't far behind. Removing the manifold or covers to access them is most of the labour, doing them as a set saves doing the job again in six months.
What if a glow plug snaps off when I try to remove it? +
It happens, particularly on engines that haven't had the plugs out in 100,000 miles. Stop and reconsider. Don't drill it out yourself unless you're prepared for the cylinder head to come off if it goes wrong. A workshop with the right tools can extract a snapped plug with the head still in place using specialist removal kits, but it's an expensive job (£200-£500 per plug). Sometimes leaving it and just running the engine on the remaining plugs is the practical answer.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →