Glow Plug/Heater Circuit B
The Powertrain Control Module (PCM) has detected a malfunction in the 'B' circuit of the diesel engine's glow plug or intake air heater system. This code is set when the voltage or resistance in the glow plug circuit B falls outside the manufacturer's expected range, indicating a failure to properly heat the cylinders for cold starting.
While the vehicle can usually still be driven, cold weather starting may become difficult or impossible. It should be diagnosed soon to prevent excessive wear on the starter and battery.
Common symptoms
- Illuminated Check Engine Light (MIL)
- Hard starting or extended cranking in cold weather
- Engine misfires or rough idling immediately after startup
- White smoke from the exhaust on startup
- Glow plug indicator light stays on longer than usual or flashes
Likely causes
- Defective glow plug(s) in circuit B
- Faulty glow plug relay or control module
- Corroded, loose, or damaged wiring in the glow plug circuit
- Blown glow plug fuse or fusible link
- Faulty engine coolant temperature sensor providing incorrect data
- Defective Powertrain Control Module (PCM)
What to check before replacing parts
Check the glow plug circuit fuses and fusible links.
Look for: A blown fuse or melted fusible link indicates a short circuit that needs to be traced before replacing the fuse.
Test the glow plug relay or module for proper operation.
Look for: Listen for a click when the key is turned on, and verify with a multimeter that voltage is being sent from the relay to the glow plugs.
Measure the resistance of the glow plugs in circuit B using a digital multimeter.
Look for: Resistance should typically be between 0.5 and 2.0 ohms; an open circuit (infinite resistance) or unusually high resistance indicates a failed glow plug.
Inspect the wiring harness and connectors for circuit B.
Look for: Look for melted insulation, corrosion at the connectors, or loose ground connections that could cause high resistance or an open circuit.
Check the voltage at the glow plug connectors during the initial key-on cycle.
Look for: The presence of battery voltage (usually for a few seconds depending on engine temperature) confirms the PCM and relay are commanding the circuit correctly.
This page explains the generic P0382 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.