The engine's Electronic Control Module (ECM) controls the engine fan speed by bypassing the engine oil pressure from the variable fan clutch. The current to the control solenoid is a pulse width modulated signal. The signal varies between 0.4 (maximum fan speed) to 1.9 Amperes (minimum fan speed).
The ECM adjusts the current to the solenoid in order to keep the fan speed within ± 50 rpm of the desired speed. The minimum fan speed is set to 450 rpm when the air conditioner is ON.
An override is available with the Caterpillar Electronic Technician (ET). This allows the fan to be manually changed from the minimum to the maximum possible speed. If the ECM detects a problem with the solenoid circuit, a diagnostic code is generated. If the ECM detects a problem with the solenoid circuit, the current to the solenoid is set to the minimum value.
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| Illustration 1 | g00909631 |
Test Step 1. Check for Connector Damage.
- Turn the keyswitch to the OFF position.
- Turn the breaker for the engine to the OFF position.
- Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
- Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).
- Check the customer connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
The connectors and wiring should be free of the following problems: damage, corrosion, abrasion and incorrect attachment.
Results:
- OK - The connectors and wiring are okay. Proceed to test step 2.
- Not OK -
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
Stop.
Test Step 2. Check for an Internal Short or for an Open at the Engine Fan Control Solenoid.
- Disconnect the solenoid connector J86/P86.
- Measure the resistance between J86-1 and J86-2.
Expected Result:
The resistance should be between 3 and 8 Ohms.
Results:
- OK - The resistance is between 3 and 8 Ohms. Proceed to test step 3.
- Not OK - The resistance is less than 3 Ohms or more than 8 Ohms. The solenoid is internally shorted or open.
Repair: Replace the solenoid.
Stop.
Test Step 3. Check the Supply Voltage at the Solenoid Connector.
- Install the Cat ET.
- Turn the breaker for the engine to the ON position.
- Turn the keyswitch to the ON position. The engine should be OFF.
- Select the parameters for the override on the Cat ET.
- Set the override for the engine fan to 100 percent.
Note: Disconnecting the connector will cause an open circuit diagnostic code to be generated. Disregard the code and delete the code after completing this test.
- Measure the voltage between J86-1 and J86-2.
- Turn the keyswitch to the OFF position. The engine should be OFF.
Expected Result:
The voltage should be greater than 3.8 VDC. The typical voltage is 8.5 VDC at normal operating temperature.
Results:
- OK - The voltage is correct.
Repair: The voltage reaches the solenoid. If the system operates correctly, check the mechanical operation of the solenoid.
Stop.
- Not OK - The voltage is incorrect. Proceed to test step 4.
Test Step 4. Check the Supply Voltage at the ECM.
- Turn the breaker for the engine to the OFF position.
- Disconnect ECM connector J2/P2.
- Remove wire F700-BU from P2-19. Install a wire jumper into the socket for P2-19.
- Remove wire E799-BR from P2-7. Install a wire jumper into the socket for P2-7.
- Turn the breaker for the engine to the ON position.
- Turn the keyswitch to the ON position. The engine should be OFF.
- Select the parameters for the override on the Cat ET.
- Set the override for the engine fan to 100 percent.
Note: Disconnecting the supply wire will generate an open circuit diagnostic code. Disregard the code and delete the code after completing this test.
- Measure the voltage at the ECM connector between the wire jumpers in P2-19 and P2-7.
- Turn the keyswitch to the OFF position. The engine should be OFF.
- Turn the breaker for the engine to the OFF position.
- Remove the wire jumpers. Replace all wires.
Expected Result:
The voltage should be greater than 3.8 VDC. The typical voltage is 8.5 VDC at normal operating temperature.
Results:
- OK - The voltage is correct. There is an open circuit or excessive resistance in the harness between the ECM and the solenoid. Proceed to test step 5.
- Not OK - The voltage is incorrect.
Repair: Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM".
Stop.
Test Step 5. Check for a Short Circuit in the Harness.
- Disconnect the ECM connector J2/P2. Disconnect the solenoid connector J86/P86.
- Measure the resistance between P86-1 and P86-2.
- Measure the resistance between P86-1 and the chassis ground.
- Measure the resistance between P86-2 and the chassis ground.
Expected Result:
The resistance should be greater than 20,000 Ohms for each measurement.
Results:
- OK - The resistance is greater than 20,000 Ohms for each measurement. The wires are not shorted to ground. Proceed to test step 6.
- Not OK - The resistance is less than 20,000 Ohms for a measurement.
Repair: The wire and/or connectors is shorted to ground or to each other. Repair the wire or replace the wire.
Stop.
Test Step 6. Check for an Open Circuit in the Harness.
- Measure the resistance between pins P86-1 and P2-19.
- Measure the resistance between pins P86-2 and P2-7.
Expected Result:
The resistance should measure less than 10 Ohms.
Results:
- OK - The resistance measures less than 10 Ohms.
Repair: There may be an intermittent problem in the harness. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".
Stop.
- Not OK - The resistance measures more than 10 Ohms.
Repair: The wire and/or connectors has excessive resistance. Repair the wire or replace the wire.
Stop.