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DTC P1490: Low Speed Fan Control Relay Circuit: Testing

  1. Turn ignition on. Using scan tool, actuate low speed radiator fan relay. If radiator fan cycles on and off, go to next step. If radiator fan does not cycle on and off, go to step  4 .
  2. With low speed radiator fan relay still being actuated, wiggle wiring harness between low speed radiator fan relay and PCM. Low speed radiator fan relay is located in engine compartment, in Power Distribution Center (PDC). For PCM location, see Figure . If wiggling causes radiator fan relay to stop cycling, repair wiring as necessary where wiggling caused cycling to stop. If wiggling does not cause radiator fan relay to stop cycling, go to next step.
  3. Turn ignition off. Visually inspect related wiring and connectors. If a problem is found, repair as necessary. If no problems are found, test is complete.
  4. Turn ignition off. Remove low speed radiator fan relay from Power Distribution Center (PDC). See Figure . Turn ignition on. Measure voltage between ground and fused ignition switch output circuit (Light Green/Black wire) at high speed radiator fan relay harness connector terminal No. 25. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open in fused ignition switch output circuit.
  5. Turn ignition off. Disconnect PCM harness connectors. See Figure . Measure resistance of low speed radiator fan relay control circuit (Yellow/Red wire) between terminal No. 29 at low speed radiator fan relay harness connector and terminal No. 55 at PCM C2 harness connector. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Yellow/Red wire.
  6. Measure resistance between ground and low speed radiator fan relay control circuit (Yellow/Red wire) at terminal No. 29 at low speed radiator fan relay harness connector. If resistance is more than 100 k/ohms, go to next step. If resistance is 100 k/ohms or less, repair short to ground in Yellow/Red wire.
  7. Install low speed radiator fan relay. Turn ignition on. Connect a jumper wire between ground and low speed radiator fan relay control circuit (Yellow/Red wire) at terminal No. 55 at PCM C2 harness connector. If low speed radiator fan relay actuates, go to next step. If low speed radiator fan relay does not actuate, replace low speed radiator fan relay.
  8. If no other possible causes are remaining, replace PCM.
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