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DTC codes / P03xx · Ignition system and misfire / P0380

P0380Glow Plug/Heater Circuit A Malfunction

P0380 is a generic powertrain code that indicates the engine control module has detected a malfunction in the glow plug heater circuit for cylinder bank A, which is the first bank of cylinders on engines with multiple banks. The computer monitors the electrical characteristics of the glow plug circuit and sets this code when the circuit does not behave as expected, such as an open circuit, short to ground, or excessive resistance.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Illuminated check engine light or glow plug warning light on the dashboard
  • Hard starting or extended cranking, especially in cold weather
  • Rough idle or misfire immediately after a cold start
  • White smoke from the exhaust during cold starts
  • Reduced fuel economy or increased emissions during warm-up
  • Often no symptoms besides the warning light, particularly in mild climates

Common causes, most likely first

  1. Failed glow plug on one or more cylinders in bank A
  2. Damaged or corroded glow plug wiring harness or connector
  3. Open or shorted glow plug control module or relay
  4. Blown fuse or fusible link in the glow plug power circuit
  5. Poor ground connection for the glow plug circuit
  6. Engine control module software issue or internal fault (less common)

How to diagnose and fix it

  1. Scan all modules for stored and pending codes to confirm P0380 is the primary fault and not a secondary code.
  2. Inspect the glow plug wiring harness and connectors for damage, corrosion, or loose connections.
  3. Check the glow plug fuse and relay, and test the relay operation with a multimeter.
  4. Measure the resistance of each glow plug in bank A and compare to specifications; replace any that are out of range.
  5. Test the glow plug control module output with a multimeter or oscilloscope to verify proper voltage and pulse width.
  6. Check for technical service bulletins or software updates for the engine control module that may address glow plug circuit faults.
  7. Clear codes and perform a road test to verify the repair, ensuring the code does not return.

Glow plug circuit faults often misdiagnosed

  • A failed glow plug is the most common cause, but technicians often replace all glow plugs unnecessarily when only one is faulty; always test each plug individually.
  • Corroded connectors at the glow plug tips can mimic a failed plug, so inspect and clean terminals before condemning the plug.
  • The glow plug control module may set P0380 even when the glow plugs themselves are good, so test the module's output signal before replacing parts.
  • On some vehicles, a weak battery or charging system fault can cause low voltage to the glow plug circuit and trigger P0380, so check battery health first.
  • P0380 refers specifically to bank A; on V-type engines, bank B faults set a different code, so do not assume all glow plugs are affected.

Can I keep driving with P0380?

You can usually drive the vehicle with P0380, but cold starting may be difficult and prolonged driving with a faulty glow plug circuit can damage the starter or battery. Avoid heavy loads and cold starts until the fault is repaired, and address the issue promptly to prevent further damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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