3500B and 3500C Locomotive Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the exhaust temperature sensors or if any one of the diagnostic codes in Table 1 is active or easily repeated.

System Operation

Use this procedure to troubleshoot any suspect problems with the following sensors:

• Left exhaust temperature sensor

• Right exhaust temperature sensor

The PWM sensors provide a signal to the engine's ECM for certain engine operating conditions. The sensors receive a 8.0 ± 0.4 VDC regulated voltage from the ECM.

The sensor's wires are routed from the ECM to the sensor connectors. The following list gives the terminal locations for the sensor connector.

• Terminal A 8 V supply

• Terminal B sensor return

• Terminal C sensor signal

The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.

Illustration 1	g01213936
Typical schematic

Illustration 2	g01213937
P1 ECM connector (P1-4) 8 V supply (P1-5) Digital return (P1-11) Left exhaust temperature (P1-12) Right exhaust temperature

Illustration 3	g01094844
Sensor connector (Pin A) Sensor supply (Pin B) Sensor return (Pin C) Signal

Illustration 4	g01259276
Left side view (1) Left exhaust temperature sensor

Illustration 5	g01259278
Right side view (2) Right exhaust temperature sensor

Test Step 1. CHECK FOR AN "ACTIVE" DIAGNOSTIC CODE

1. Connect Caterpillar Electronic Technician (ET) to the service tool connector.

2. Monitor the diagnostic codes on Cat ET. Check and record any diagnostic codes.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

3. Determine if a diagnostic code has occurred several times.

   Note: A diagnostic code that is logged several times is an indication of an intermittent problem. Most intermittent problems are the result of a bad connection between a socket and a pin in a connector or a bad connection between a wire and a terminal.

4. Determine if a -8 diagnostic code is active for one of the exhaust temperature sensors.

Expected Result:

No diagnostic code is active for the exhaust temperature sensors.

Results:

• OK - No diagnostic codes are active.

  Repair: If the problem is intermittent, refer to Troubleshooting, "Inspecting Electrical Connectors" for the correct procedures for inspecting electrical connectors.

  STOP

• Not OK - A -8 diagnostic code is active or the diagnostic code is logged several times. Proceed to Test Step 2.

Test Step 2. CHECK THE DIGITAL SUPPLY VOLTAGE AT THE SENSOR CONNECTOR

1. Disconnect the suspect sensor(s) at the sensor connector:

2. Measure the voltage on the ECM side of the sensor connector between pin A and pin B for the suspect sensor(s).

Expected Result:

The supply voltage is 8.0 ± 0.4 VDC.

Results:

• OK - The supply voltage is 8.0 ± 0.4 VDC. Proceed to Test Step 4.

• Not OK - The supply voltage is not 8.0 ± 0.4 VDC. Proceed to Test Step 3.

Test Step 3. CHECK THE DIGITAL SUPPLY VOLTAGE AT THE ECM

1. Turn the breaker for the ECM to the OFF position.

2. Remove the supply wire from P1-4. Install a wire jumper into the socket for P1-4.

3. Turn the breaker for the ECM to the ON position.

4. Measure the voltage between the wire jumper in terminal P1-4 and engine ground.

5. Turn the breaker for the ECM to the OFF position.

6. Remove the wire jumper and reconnect all wires. Reconnect ECM connector J1/P1.

Expected Result:

The supply voltage is 8.0 ± 0.4 VDC.

Results:

• OK - The supply voltage is 8.0 ± 0.4 VDC. The supply voltage at the ECM is correct. There is a problem in the wiring between the ECM and the sensor connector. Repair the connectors or wiring and/or replace the connectors or wiring.

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

  STOP

• Not OK - The supply voltage is not 8.0 ± 0.4 VDC. The voltage at the ECM is not correct.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  STOP

Test Step 4. CHECK THE SENSOR'S DUTY CYCLE AT THE SENSOR CONNECTOR

1. Turn the breaker for the ECM to the OFF position.

2. Remove the suspect sensor's signal wire from pin C of the sensor connector.

3. Reconnect the suspect sensor connector.

4. Turn the breaker for the ECM to the ON position.

5. Measure the duty cycle between the sensor's signal wire and pin B of the sensor connector.

   Note: Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

6. Turn the breaker for the ECM to the OFF position.

7. Replace the sensor's signal wire and reconnect the sensor.

Expected Result:

The duty cycle is between 10 to 90 percent.

Results:

• OK - The duty cycle is correct. Proceed to Test Step 5.

• Not OK - The duty cycle is incorrect.

  Repair: Replace the sensor. Verify that no diagnostic codes are active for the suspect sensor before permanently installing the sensor.

  STOP

Test Step 5. CHECK THE SENSOR'S DUTY CYCLE AT THE ECM

1. Turn the breaker for the ECM to the OFF position.

2. Remove the suspect signal wire for the sensor from ECM connector P1. Refer to Illustration 1 for the terminal locations for the ECM connector.

3. Turn the breaker for the ECM to the ON position.

4. Measure the duty cycle between the sensor's signal wire and the sensor's return wire.

   Note: Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.

5. Turn the breaker for the ECM to the OFF position. Reconnect all wires.

Expected Result:

The duty cycle is between 10 to 90 percent.

Results:

• OK - The duty cycle is correct.

  Repair: Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "Replacing the ECM".

  STOP

• Not OK - The duty cycle is not correct.

  Repair: There is a problem in the wiring between the ECM and the connector for the sensor. Repair the connectors and/or wiring between the ECM and the connector for the sensor.

  STOP