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DTC P1490: Low Speed Fan Control Relay Circuit: Testing

  1. Turn the ignition on. With the DRBIII(R), actuate the low speed radiator fan relay. Is the low speed radiator fan relay operating? If yes, go to next step. If no, go to step  4 .
  2. Wiggle the wiring harness from the low speed fan relay to the PCM while the DRBIII(R) is actuating the low speed fan relay. Did the low speed fan relay stop when wiggling the wiring harness? If yes, repair as necessary. If no, go to next step.
    3. 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.
  3. Conditions that set 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(R) 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(R) Freeze Frame information to identify under what conditions the DTC set.
    • Refer to any Technical Service Bulletin (TSB) that may apply.
    • 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.

  4. Turn the ignition off. Remove the low speed radiator fan relay from the Power Distribution Center (PDC). Turn the ignition on. Measure the voltage on the fused ignition switch output circuit in the PDC. Is the voltage more than 11.0 volts? If yes, go to next step. If no, repair the fused ignition switch output circuit as necessary. Check and replace any open fuses.
  5. Turn the ignition off. Measure the resistance of the low speed radiator fan relay between the fused ignition switch output terminal and the low speed radiator fan relay control terminal (component side). Is the resistance 60-80 ohms? If yes, go to next step. If no, replace the low speed radiator fan relay.
  6. Disconnect the PCM harness connectors. Measure the resistance of the low speed radiator fan relay control circuit between the PDC and the PCM harness connector. Is the resistance less than 5.0 ohms? If yes, go to next step. If no, repair the low speed radiator fan relay control circuit for an open.
  7. Measure the resistance of the low speed radiator fan relay control circuit in the PDC to ground. Is the resistance less than 100 ohms? If yes, repair the low speed radiator fan relay control circuit for a short to ground If no, go to next step.
  8. There are no possible causes remaining, replace the PCM.
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