3512 and 3516 EUI Engines for 784B, 785B, 789B and 793B Off-Highway Trucks Caterpillar

The engine fan speed sensor provides the signal of fan speed to the engine's Electronic Control Module (ECM). The ECM controls fan speed by varying the current to the fan control solenoid. The ECM controls fan speed within ± 50 rpm of the desired fan speed. The desired fan speed is based on the following conditions: coolant temperature, aftercooler temperature, brake oil temperature, engine speed and actual fan speed.

The engine fan speed sensor receives a supply voltage of 12.7 ± 1.0 VDC from the engine's ECM. The sensor outputs a frequency that is directly proportional to fan speed. The sensor generates a signal pulse for each revolution of the fan. The output frequency varies between 0.83 Hz to 30 Hz over a speed range between 50 rpm and 1800 rpm.

Illustration 1	g00935113

Test Step 1. Check for Connector Damage.

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the ECM connector J1/P1 and the machine connector J2/P2. Inspect all of the other connectors. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.

4. Check the ECM connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).

5. Check the machine connector (allen head screw) for the proper torque of 2.25 ± 0.25 N·m (20 ± 2 lb in).

6. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

The connectors and wiring are 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 - The connectors and/or wiring need repair.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.

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

1. Connect the Cat ET to the cab service tool connector J31. Start Cat ET.

2. Turn the keyswitch to the START position. Accelerate the engine to high idle. Use Cat ET to set the engine fan speed to 800 rpm.

3. Observe the status of the engine fan speed on Cat ET.

Expected Result:

The engine fan speed is within ± 50 rpm of the 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 problem. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  Stop.

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

Test Step 3. Check the Sensor Supply Voltage at the Connector for the Engine Fan Speed Sensor.

1. Turn the keyswitch to the OFF position. The engine should be off.

2. Disconnect the connector for the engine fan speed sensor J47/P47.

   Note: If you remove the sensor common from a sensor, an open circuit diagnostic code will be generated for that sensor. Troubleshoot the original code. Delete the logged diagnostic code when you are finished.

3. Turn the keyswitch to the ON position.

4. Measure the sensor supply voltage at the connector between P47-A and P47-B.

Expected Result:

The voltage is 12.7 ± 1.0 VDC.

Results:

• OK - The voltage is 12.7 ± 1.0 VDC. The supply voltage is reaching the sensor. Proceed to Test Step 4.

• Not OK - The voltage is not 12.7 ± 1.0 VDC. The supply voltage is not reaching the sensor. Proceed to Test Step 6.

Test Step 4. Check the Signal Frequency for the Engine Fan Speed Sensor at the Sensor Connector.

1. Turn the keyswitch to the OFF position. The engine should be off.

2. Remove the signal wire from J47-C at the connector for the fan speed sensor.

3. Reconnect the connector for the fan speed sensor.

4. Turn the keyswitch to the START position. Accelerate the engine to high idle. Use Cat ET to set the engine fan speed to 800 rpm.

5. Measure the frequency between the wire that was removed from J47-C and the digital return pin P47-B.

6. Turn the keyswitch to the OFF position. The engine should be off.

7. Reconnect all connectors and wires.

Expected Result:

The frequency is approximately 13.33 Hz.

Results:

• OK - The frequency is approximately 13.33 Hz. Proceed to Test Step 5.

• Not OK - The frequency is not approximately 13.33 Hz.

  Repair: Replace the engine fan speed sensor. Verify that the new sensor is operating correctly.

  Stop.

Test Step 5. Check the Signal Frequency for the Engine Fan Speed Sensor at the ECM.

1. Turn the keyswitch to the OFF position. The engine should be off.

2. Remove the signal wire F732-PK from P1-38 at ECM connector P1.

3. Reconnect ECM connector P1.

4. Turn the keyswitch to the START position. Accelerate the engine to high idle. Use Cat ET to set the engine fan speed to 800 rpm.

5. Measure the frequency between wire F732-PK and the digital return pin P1-09.

6. Turn the keyswitch to the OFF position. The engine should be off.

7. Reconnect all connectors and wires.

Expected Result:

The frequency is approximately 13.33 Hz.

Results:

• OK - The frequency is approximately 13.33 Hz.

  Repair: A valid signal is present at the ECM. The ECM is not reading the signal properly. Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM.".

  Stop.

• Not OK - The frequency is not approximately 13.33 Hz. There is a problem in the wiring between the ECM and the sensor connector. Proceed to Test Step 7.

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

1. Remove wire A700-OR from P1-51 at the ECM connector P1. Install a wire jumper into the socket P1-51.

2. Remove wire 998-BR from P1-09 at the ECM connector P1. Install a wire jumper into the socket P1-09.

   Note: If you remove the sensor common from the ECM, an open circuit diagnostic code will be generated for all sensors that use the sensor common. Troubleshoot the original code. Delete the logged diagnostic code when you are finished.

3. Turn the keyswitch to the ON position.

4. Measure the sensor supply voltage between the wire jumpers in P1-51 and P1-09.

5. Turn the keyswitch to the OFF position. The engine should be off.

6. Remove all wire jumpers. Reconnect all connectors and wires.

Expected Result:

The voltage is 12.7 ± 1.0 VDC.

Results:

• OK - The voltage is 12.7 ± 1.0 VDC. There is a problem in the harness between the ECM and the connector for the fan speed sensor. Proceed to Test Step 7.

• Not OK - The voltage is not 12.7 ± 1.0 VDC.

  Repair: Perform the diagnostic functional test Troubleshooting, "Electrical Power Supply".

  Stop.

Test Step 7. Check for a Short Circuit in the Wiring Harness.

1. Turn the keyswitch to the OFF position.

2. Disconnect ECM connectors J1/P1.

3. Disconnect the connector for the fan speed sensor J47/P47.

4. Measure the resistance between P1-51 and P1-09 at the ECM connector.

5. Measure the resistance between P1-51 and P1-38 at the ECM connectors.

6. Measure the resistance between P1-51 and the engine ground.

7. Measure the resistance between P1-38 and the engine ground.

8. Measure the resistance between P1-09 and the engine ground.

Expected Result:

The resistance is more than 20,000 Ohms.

Results:

• OK - The resistance is more than 20,000 Ohms. Proceed to Test Step 8.

• Not OK - There is a short circuit in the harness or in the connectors.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.

Test Step 8. Check for an Open Circuit in the Wiring Harness.

1. Use a suitable piece of wire to short P47-A and P47-C together at the sensor connector.

2. Measure the resistance between P1-51 and P1-38 at the ECM connector P1.

3. Use a suitable piece of wire to short P47-B and P47-C together at the sensor connector.

4. Measure the resistance between P1-09 and P1-38 at the ECM connector P1.

5. Remove the wire shorts and reconnect all connectors.

Expected Result:

The resistance is less than 5 Ohms through the wires.

Results:

• OK - The resistance is less than 5 Ohms through the wires.

  Repair: The problem may be intermittent. If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".

  Stop.

• Not OK - The resistance is greater than 5 Ohms through the wires. There is an open circuit in the harness or in the connectors.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring.

  Stop.