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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 step  3.
    2. WARNING: When, the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
  2. The conditions that set the DTC are not present at this time. The following list may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Turn the ignition off. Refer to any Technical Service Bulletins (TSB) that may apply. Turn ignition on, engine not running. With the DRBIII®, actuate the Radiator Fan Relay and wiggle the related wiring harness. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
  3. Turn the ignition off. Disconnect the Radiator Fan Relay harness connector. Using a 12-volt test light connected to 12 volts, probe the Ground circuit in the Radiator Fan Relay harness connector. Does the test light illuminate? If yes, go to next step. If no, repair the Ground circuit for an open.
    4. NOTE: Inspect the Radiator Fan fuse (fuse No. 2) located in the PDC.
  4. Measure the voltage of the Fused B+ Output circuit in the Radiator Fan harness 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 Fused B+ circuit.
  5. Ensure the ignition is off. Disconnect the PCM harness connectors. Measure the resistance of the Radiator Fan Relay Control circuit between the Radiator Fan Relay harness connector and the PCM harness connector. Is the resistance below 5.0 ohms? If yes, repair the open in the Radiator Relay Control circuit between the PCM and PDC. If no, go to next step.
  6. 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.
  7. 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.
  8. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
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