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Home >> Jeep >> 2003 >> Liberty Limited, 4WD, Part Time, 42RLE >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P1491: Rad Fan Control Relay Circuit >> Testing

DTC P1491: Rad Fan Control Relay Circuit: Testing

  1. Turn ignition on, engine not running. With the DRBIII®, actuate the Radiator Fan Relay. Are both Radiator Fans operating? If yes, go to next step. If no, go to next step.
  2. Turn the ignition off. Disconnect the Radiator Fan Relay. Using a 12-volt test light connected to ground, probe the (C24) Fused B+ circuit of the Cooling Fan Relay connector. Is the voltage above 11.0 volts? If yes, go to next step. If no, repair the open or short to ground in the (C24) Fused B+ circuit. Inspect the related fuse and repair as necessary.
  3. Using a 12-volt test light connected to 12-volts, probe the (Z212) Ground circuit in the Cooling Fan Relay harness connector. Does the test light illuminate brightly? If yes, go to the next step. If no, repair the open in the (Z212) Ground circuit.
  4. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance of the (K173) Radiator Fan Relay Control circuit between the Radiator Fan Relay connector and the PCM harness connector. Is the resistance below 5.0 ohms? If yes, repair the open in the (K173) Radiator Relay Control circuit between the PCM and PDC. If no, go to next step.
  5. Measure the resistance of the Radiator Fan Relay Control circuit in the Radiator Fan Relay harness connector to ground. Is the resistance below 100 ohms? If yes, repair short to ground. If no, go to next step.
  6. Reconnect radiator fan relay connector. Connect a jumper wire to the Radiator Fan Relay Control circuit in the PCM harness connector. Briefly tap other end of jumper wire to ground and observe radiator fan operation. Did the Radiator Fans actuate? If yes, go to next step. If no, replace the Radiator Fan Relay.
    7. NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
  7. Using the wiring diagram as a guide, inspect the wire harness and connectors. Pay particular attention to all power and ground circuits. If there are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
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