No Low Speed Operation But Fan 1 (Left) Operates At High Speed (P0480)
This would be a symptom of a low speed control issue. Radiator fan 1 high relay is supplied fused B+ from the same fuse as the low speed relay.
- Turn the ignition on. Using a 12-volt test light connected to ground, back probe the low speed fan control circuit at the PDC. This is the circuit that connects to both radiator fan relays in the PDC. Grounding either connection should ground and energize both relays. Both fans should run at low speed with the control circuit grounded.
- If both fans run at low speed with the control circuit grounded, it would indicate an open control circuit or faulty PCM. Continue to step 2.
- If the fans do not run with the control circuit grounded, It would indicate faulty relays or circuit issue in the PDC. Continue to step 3.
- The control circuit and PCM can be checked one of two ways.
- Connect the GPEC adaptor in-line with the PCM harness connector. The harness should be connected to the PCM. Using a voltmeter, probe and measure the voltage on the on the (N112) low speed control circuit at the GPEC adaptor. When the low speed control circuit is not being commanded and grounded by the PCM, battery voltage should be passing through the relay coils to the control circuit. Using the scan tool, select the Rad/Cond Cooling Fan Relay #1 Control State actuator. This should ground the control circuit inside the PCM and the voltage should no longer be present.
- If voltage is not present at the control circuit with the relays not being commanded on, repair the low speed control circuit for an open.
- If voltage is still present when the Rad/Cond Cooling Fan Relay #1 Control State actuator is activated, replace the PCM in accordance with the Service Information.
- Disconnect the PCM harness connector and remove the low speed fan relays from the PDC to isolate the control circuit. Measure the resistance of the (N112) low speed control circuit between each relay connector and the GPEC Adaptor. Should be less than 3.0 Ohms.
- If the resistance is above 3.0 Ohms, repair the control circuit for an open or high resistance.
- If the resistance is less than 3.0 Ohms, replace the PCM in accordance with the Service Information.
- Connect the GPEC adaptor in-line with the PCM harness connector. The harness should be connected to the PCM. Using a voltmeter, probe and measure the voltage on the on the (N112) low speed control circuit at the GPEC adaptor. When the low speed control circuit is not being commanded and grounded by the PCM, battery voltage should be passing through the relay coils to the control circuit. Using the scan tool, select the Rad/Cond Cooling Fan Relay #1 Control State actuator. This should ground the control circuit inside the PCM and the voltage should no longer be present.
- Use the information provided in the fan relay component functional description to test the operation of the relay coils.
- If the relays test good, check the power supply connection to the PDC and all other fuses in the PDC. If the power supply connection and fuses check good, replace the Power Distribution Center in accordance with the Service Information.
- If the relays are faulty, replace the relays and retest.