3412E Engine for Caterpillar Built Machines Cooling Fan Speed - Test Caterpillar

System Operation Description:

Use this procedure to troubleshoot the electrical system if a problem is suspected with the cooling fan speed sensor or if any one of the diagnostic codes in Table 1 is active or easily repeated.

The fan speed sensor is a digital sensor that provides a speed signal from the engine cooling fan to the Electronic Control Module (ECM). The ECM controls the speed of the fan by varying the current to the fan speed solenoid. The ECM attempts to keep the fan within ± 50 rpm of the desired fan speed.

The fan speed sensor receives a regulated 8.0 ± 0.5 VDC supply voltage from the ECM. The fan speed sensor provides a pulse width modulated signal to the ECM that represents the speed of the fan. The frequency range of the output represents fan speeds from 50 rpm to 1800 rpm.

Note: Refer to Troubleshooting, "Sensor Supply - Test" if the ECM has detected a problem with the digital sensor supply voltage.

Illustration 1	g01393234
Schematic for the fan speed sensor

Test Step 1. Inspect Electrical Connectors and Wiring

1. Remove electrical power from the ECM.

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Illustration 2	g01139425
ECM (1) J1/P1 connectors (2) J2/P2 connectors

2. Thoroughly inspect ECM connector J1/P1, ECM connector J2/P2, and all other connectors in the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

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Illustration 3	g01394757
P1 terminals that are associated with the cooling fan speed (P1-29) Sensor return (P1-35) +8 V digital supply

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Illustration 4	g01394760
P2 terminal that is associated with the cooling fan speed (P2-25) Engine fan speed

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the Cat Data Link.

4. Check the allen head screw on each ECM connector for the proper torque. Also, check the allen head screw on the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

Expected Result:

All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The harness and connectors appear to be OK. Proceed to Test Step 2.

• Not OK - There is a problem with the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled. Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Status of the Engine Fan Speed with AVSpare Electronic Technician (ET)

1. Connect Cat ET to the service tool connector.

2. Restore electrical power to the ECM. Start the engine.

3. Compare the status for "Engine Fan Speed" to the status for "Desired Engine Fan Speed" on ET.

4. Remove electrical power from the ECM.

Expected Result:

"Engine Fan Speed" is within ± 50 rpm of "Desired Engine Fan Speed".

Results:

• OK - The engine fan speed is within the desired rpm range.

  Repair: The sensor is operating correctly. There may be an intermittent electrical problem in a connector or in the harness. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The engine fan speed is not within the desired rpm range. Proceed to Test Step 3.

Test Step 3. Check the Digital Sensor Supply Voltage at the Sensor Connector

1. Disconnect the connector for the engine cooling fan speed sensor.

2. Restore electrical power to the ECM.

3. Measure the voltage across terminal A (+8 V digital supply) and terminal B (sensor return).

4. Disconnect the connector for the engine cooling fan speed sensor.

5. Remove electrical power from the ECM.

Expected Result:

The digital sensor supply voltage should be 8.0 ± 0.5 VDC.

Results:

• OK - The supply voltage is reaching the sensor. Proceed to Test Step 4.

• Not OK - The supply voltage is not reaching the sensor. Proceed to Test Step 5.

Test Step 4. Check for Shorts in the Harness From the Fan Speed Sensor to the ECM

1. Disconnect the ECM connectors J1/P1 and J2/P2.

2. Disconnect the connector for the engine cooling fan speed sensor.

3. Measure the resistance between terminal P1-35 (+8 V digital supply) and chassis ground.

4. Measure the resistance between terminal P1-35 (+8 V digital supply) and all of the other terminals on the P1 connector.

5. Measure the resistance between terminal P1-35 (+8 V digital supply) and all of the terminals on the P2 connector.

6. Measure the resistance between terminal P2-25 (engine fan speed) and chassis ground.

7. Measure the resistance between terminal P2-25 (+8 V digital supply) and all of the other terminals on the P2 connector.

8. Measure the resistance between terminal P2-25 (+8 V digital supply) and all of the terminals on the P1 connector.

Expected Result:

The resistance for each measurement indicates an open circuit.

Results:

• OK - The resistance measurement indicates an open circuit. Proceed to Test Step 5.

• Not OK - The resistance measurement indicates there is a short between the ECM and the fan speed sensor.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  STOP

Test Step 5. Check for Open Circuits in the Harness From the Fan Speed Sensor to the ECM

1. Remove electrical power from the ECM.

2. Disconnect the ECM connectors J1/P1 and J2/P2.

3. Use a suitable piece of wire to short terminal P1-35 (+8 V digital supply) and terminal P1-29 (sensor return).

4. Disconnect the connector for the engine cooling fan speed sensor.

5. Measure the resistance between terminal A (+8 V digital supply) and terminal B (sensor return).

6. Use a suitable piece of wire to short terminal P2-25 (+8 V digital supply) and terminal P1-29 (sensor return).

7. Measure the resistance between terminal C (engine fan speed) and terminal B (sensor return).

Expected Result:

The resistance measurements do not indicate an open circuit.

Results:

• OK - The resistance measurements do not indicate an open circuit. Proceed to Test Step 6.

• Not OK - There is an open circuit in the wiring harness between the fan speed sensor and the ECM.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  STOP

Test Step 6. Check the Digital Sensor Supply Voltage at the ECM

1. Remove electrical power from the ECM.

2. Disconnect the J1/P1 ECM connector.

3. Fabricate jumper wires that are long enough to be used to measure the supply voltage at the ECM connector. Crimp connector sockets to one end of each jumper wire.

4. Remove the wires from terminal P1-35 (digital supply) and terminal P1-29 (sensor return). Install a jumper wire into each of these terminal locations.

5. Connect the J1/P1 ECM connector.

6. Restore electrical power to the engine ECM.

7. Measure the voltage between the jumper wire in terminal P1-35 (digital supply) and the jumper wire in terminal P1-29 (sensor return).

8. Remove electrical power from the ECM.

Expected Result:

The digital sensor supply voltage should be 8.0 ± 0.5 VDC.

Results:

• OK - The ECM is producing a valid supply voltage. Proceed to Test Step 7.

• Not OK - The ECM is not producing a valid supply voltage.

  Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace".Verify that the repair eliminates the problem.

  STOP

Test Step 7. Check the Signal Frequency at the ECM

1. Remove electrical power from the ECM.

2. Disconnect the J2/P2 ECM connector. Remove the wire from terminal P2-25 (engine fan speed).

3. Restore electrical power to the ECM. Start the engine.

4. Accelerate the engine to high idle.

5. Use ET to set the desired fan speed to 800 rpm.

6. Measure the frequency of the signal between terminal P2-25 (engine fan speed) and chassis ground.

7. Remove electrical power from the ECM.

Expected Result:

The frequency is approximately 13.3 Hz.

Results:

• OK - The frequency is approximately 13.3 Hz. Proceed to Test Step 8.

• Not OK - The frequency is not approximately 13.3 Hz. The fan speed sensor is faulty.

  Repair: Replace the fan speed sensor.Verify that the repair eliminates the problem.

  STOP

Test Step 8. Check the Status of the Engine Fan Speed on ET

1. Restore electrical power to the ECM. Start the engine.

2. Accelerate the engine to high idle.

3. Compare the status for "Engine Fan Speed" to the status for "Desired Engine Fan Speed" on ET.

4. Remove electrical power from the ECM.

Expected Result:

"Engine Fan Speed" is within the acceptable range and "Engine Fan Speed" is within 50 rpm of "Desired Engine Fan Speed".

Results:

• OK - The fan speed is within the acceptable range. The sensor is operating correctly.

  Repair: There may be an intermittent problem. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The fan speed is not within the acceptable range. There is a problem with the fan speed solenoid, or there is a problem with the fan motor.

  Repair: Refer to Troubleshooting, "Cooling Fan Control - Test".

  STOP