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Checking The Cooling Fan Operation





CHECKING THE COOLING FAN OPERATION





For a complete wiring diagram, refer to the Wiring Information.

Cooling Fan Modes of Operation

The two speed cooling fan system uses two relays and a radiator fan resistor to control the cooling fan operation. The two relays are the High Fan Relay, Lo-Hi Fan Relay. During low speed mode, the cooling fan operates in series with the Radiator Fan Resistor, limiting the 12 Volt source the Radiator Fan Module. During high speed mode, the cooling fan motor receives a battery voltage feed directly from the High Speed Radiator Fan Relay.

During low speed mode: The PCM grounds the (N201) Fan Relay Control circuit, closing the relay to connect the Cooling Fan 12 Volt Supply circuit to the (N23) Cooling Fan Motor 1 Output circuit. The (N23) Cooling Fan Motor 1 Output circuit supplies 12 Volts to the Radiator Fan Resistor. Current flows through the resistor and out the (N24B) Rad Fan Relay Output circuit. The current is sent back to the PDC and is spliced into the (N24A) Rad Fan Relay Output circuit which goes directly to the Radiator Fan Module. The (Z904) Ground circuit provides the ground path for the Cooling Fan series circuit.

During High speed mode: The PCM grounds the (N112) Fan Relay Control circuit and the (N112) Fan Relay Control circuit, closing the High Speed Radiator Fan Relay. The Cooling Fan 12 Volt Supply circuit connects to the (N24A) Rad Fan Relay Output circuit and provides 12 Volts to Radiator Fan Module. The (Z904) Ground circuit provides the ground for Radiator Fan Module.

1. RADIATOR FAN 40 AMP FUSE

NOTE: Diagnose and repair any Cooling Fan Relay control circuit DTCs before proceeding with this test.

1. Inspect the 40 Amp Radiator Fan fuse for an open condition.

Is the the fuse open?

Yes

- Inspect the circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 2

2. FUSED IGNITION CIRCUITS
1. Remove both Radiator Fan Relays.
2. Turn the ignition on.
3. Using a 12-volt test light connect to ground, check the Fused Ignition circuit at the relay terminals.

Does the test light illuminate brightly?

Yes

- Go To 3

No

- Repair the fused ignition circuit for a short to ground or open condition. Inspect the related fuse.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

3. RADIATOR FAN RELAYS
1. Install known good relays in place of the existing relays.
2. Using a scan tool, actuate the low speed relay.
3. Using a scan tool, actuate the high speed relay.

NOTE: During high speed actuation the Cooling Fan Motors are easily audible.

Does the fan operate in both speeds?

Yes

- Replace the relay found to be causing the inoperative radiator fan.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 4

4. (N23) CIRCUIT OPEN OR SHORTED TO GROUND




1. Turn the ignition off.
2. Disconnect the Radiator Fan Resistor.
3. Turn the ignition on.
4. Make sure both relays are installed.
5. Using a scan tool, actuate the Low Speed (No.1) Relay.
6. Using a 12-Volt test light connected to ground, probe the (N23) Low Speed Rad Fan Control Output circuit at the Resistor harness connector.

NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.

Is the test light illuminated and bright?

Yes

- Go To 5

No

- Repair the (N23) Low Speed Rad Fan Control Output circuit for an open or short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

5. EXCESSIVE RESISTANCE IN THE (N24B) RAD FAN RELAY OUTPUT CIRCUIT
1. Stop the actuation.
2. Turn the ignition off.
3. Measure the resistance in the (N24B) Rad Fan Relay Output circuit from the Radiator Fan Resistor harness connector to the PDC C4 harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 6

No

- Repair the open or excessive resistance in the (N24B) Rad Fan Relay Output circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

6. (N24B) RAD FAN RELAY OUTPUT CIRCUIT SHORTED TO GROUND




1. Measure the resistance between ground and the (N24B) Rad Fan Relay Output circuit from the Radiator Fan Resistor harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Repair the short to ground in the (N24B) Rad Fan Relay Output circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 7

7. EXCESSIVE RESISTANCE IN THE (N24A) RAD FAN RELAY OUTPUT CIRCUIT
1. Disconnect the Radiator Fan Module harness connector.
2. Measure the resistance in the (N24A) Rad Fan Relay Output circuit from the Radiator Fan Module harness connector to the PDC C4 harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 8

No

- Repair the open or excessive resistance in the (N24A) Rad Fan Relay Output circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

8. (N24A) RAD FAN RELAY OUTPUT CIRCUIT SHORTED TO GROUND




1. Measure the resistance between ground and the (N24B) Rad Fan Relay Output circuit from the Radiator Fan Module harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Repair the short to ground in the (N24A) Rad Fan Relay Output circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 9

9. CHECK THE (Z904) GROUND CIRCUIT




1. Using a 12-Volt test light connected to 12 Volts, probe the (Z904) Ground circuit at the Radiator Fan Module harness connector.

NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.

Is the test light illuminated and bright?

Yes

- Go To 10

No

- Repair the (Z904) Ground circuit for an open.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

10. POWER DISTRIBUTION CENTER (PDC)




1. Connect the PDC C4 harness connector.
2. Ignition on, engine not running.
3. Measure the resistance from the (N24) Rad Fan Relay Output circuit from the Radiator Fan Resistor harness connector to the Radiator Fan Module harness connector.

Is the resistance above 10 Ohms?

Yes

- Replace the PDC.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Replace the Radiator Fan Module.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

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