P0380 — Glow Plug/Heater Circuit "A" Malfunction

What P0380 means

On a diesel, the engine control unit switches the glow plugs through a relay or a control module and monitors current and voltage in that circuit. P0380 is stored when circuit A reads outside the expected range, such as an open, a short, excessive resistance or no response from the module. Glow plugs warm the combustion chambers to help cold starts.

Symptoms

• Check Engine light on
• Hard starting, especially when cold
• Glow plug indicator stays on longer than normal or flashes
• Rough idle after a cold start
• White or gray smoke at startup
• Longer cranking time

Possible causes

1. Faulty glow plug relay or glow plug control module
2. Damaged or corroded wiring and connectors in the glow plug circuit
3. One or more failed glow plugs
4. Blown glow plug fuse
5. Damaged wiring harness under the valve cover
6. ECM output driver fault (uncommon)

How to diagnose

1. Scan for codes and freeze frame data and note any related power or sensor codes
2. Check the glow plug fuse and fusible link
3. Inspect wiring and connectors at the relay, module and plugs for corrosion, breaks and heat damage
4. Verify power and ground at the relay or module with the key on
5. Test the relay for a click and voltage drop across its contacts
6. Measure each glow plug's resistance and compare it to the engine's specification
7. Inspect the valve cover harness for chafing or shorts to ground
8. Check the control signal from the ECM to the relay or module

Common fixes

• Replace the faulty glow plug relay
• Replace failed glow plugs, preferably as a set
• Repair or replace damaged wiring and connectors
• Replace the glow plug control module
• Replace the fuse once the cause of the overload is fixed

Questions and answers

Can I drive with a P0380 code?

Usually yes, since the engine often starts fine when warm. Cold starts can get difficult, so fix it soon to avoid straining the battery and starter.

What most often causes P0380?

The usual causes are a bad glow plug relay or control module, poor wiring or connections, and burned-out glow plugs. Start with the fuse and a resistance test of the plugs.

Should I replace all glow plugs at once?

If one has failed, the others are usually just as worn. Many mechanics replace the full set, but base the decision on your resistance measurements.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.