WOMS
P code powertrain Medium severity

P1389 Glow Plug Circuit High Side Low Input

The OBD2 code P1389 indicates a problem with the glow plug circuit, specifically that the high side control (typically a relay or transistor) is receiving a low input signal when it should be activated, suggesting a...

Definition

The OBD2 code P1389 indicates a problem with the glow plug circuit, specifically that the high side control (typically a relay or transistor) is receiving a low input signal when it should be activated, suggesting a potential issue with the glow plug system or its control circuit

Common causes

  • Faulty glow plug
  • Bad glow plug relay
  • Open or shorted wiring in the glow plug circuit
  • Poor ground connection
  • Faulty engine control module (ECM)
  • Corroded or damaged connectors
  • Blown fuse in the glow plug circuit

Common misdiagnoses

  • Faulty glow plugs
  • Bad glow plug relay
  • Wiring issues or shorts in the circuit
  • Faulty engine control module (ECM)
  • Incorrectly installed or damaged connectors
  • Battery or charging system problems
  • Fuel system issues
  • Injector problems

Troubleshooting steps

  1. 1. Check the Code and Freeze Frame Data

    Use an OBD-II scanner to confirm the P1389 code and check for any additional codes that may provide more context

  2. 2. Review freeze frame data to understand the conditions under which the code was set

  3. 3. Inspect the Glow Plugs

    Visual Inspection: Check the glow plugs for physical damage or corrosion

  4. 4. Resistance Test

    Use a multimeter to measure the resistance of each glow plug. A typical reading should be between 0.5 to 2 ohms. If any glow plug shows an open circuit (infinite resistance), it may need to be replaced

  5. 5. Check the Glow Plug Relay

    Inspect the glow plug relay for proper operation. A faulty relay can prevent the glow plugs from receiving power

  6. 6. Test the relay by applying power directly to it and checking if it activates

  7. 7. Examine Wiring and Connectors

    Inspect the wiring harness and connectors associated with the glow plugs and relay for signs of damage, corrosion, or loose connections

  8. 8. Repair or replace any damaged wiring or connectors

  9. 9. Test the Power Supply

    Use a multimeter to check for voltage at the glow plug relay and at the glow plugs themselves when the ignition is turned on

  10. 10. Ensure that the glow plugs are receiving the correct voltage (typically around 12 volts)

  11. 11. Check the Engine Control Module (ECM)

    If all other components are functioning correctly, the issue may lie with the ECM. Check for any software updates or known issues with the ECM related to the glow plug circuit

  12. 12. If necessary, perform a reprogramming or replacement of the ECM

  13. 13. Inspect the Fuses

    Check the fuses related to the glow plug circuit. A blown fuse can interrupt power to the glow plugs

  14. 14. Clear the Code and Test Drive

    After performing repairs, clear the code using the OBD-II scanner and take the vehicle for a test drive to see if the code reappears

  15. 15. Consult Technical Service Bulletins (TSBs)

    Look for any TSBs related to the P1389 code for your specific vehicle make and model, as there may be known issues or fixes

  16. 16. Seek Professional Help

    If the issue persists after following these steps, consider consulting a professional mechanic or technician who has experience with diesel engines and glow plug systems. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P1389 code