3524B Engines for Off-Highway Trucks Caterpillar

The Digital Sensor Supply provides power to all digital sensors. The Electronic Control Module (ECM) supplies 8.0 ± 0.4 VDC to each digital sensor connector pin "A". The digital sensor return is used as the return line for the digital sensors, speed/timing sensors, and the throttle position sensor to the ECM. The digital return line is from the ECM connector J1/P1 to each digital sensor connector pin "B". The digital sensor supply is output short circuit protected. A short circuit to the battery will not damage the circuit inside the ECM. The digital sensors are NOT protected from overvoltage.

The following list contains a description of the Digital Sensors that are found on the engine.

Left Exhaust Temperature Sensor - The ECM uses the signal from the sensor to monitor left exhaust temperature. The sensor is mounted in the left exhaust manifold before the turbocharger. The sensor's output frequency is 500 Hz with a pulse width that varies with the exhaust temperature. The output signal is referred to as a Duty Cycle or as a Pulse Width Modulated signal. The output signal is expressed as a percentage between 0 and 100 percent. The Caterpillar Electronic Technician (ET) will display the exhaust temperature as a value between 49 °C to 850 °C (120 °F to 1562 °F). If the actual temperature is between −40 °C to 49 °C (−40 °F to 120 °F), the display will read 30 °C (86 °F). If the temperature is above 851 °C (1564 °F), the display will read 851 °C (1564 °F).

Right Exhaust Temperature Sensor - The ECM uses the signal from the sensor to monitor right exhaust temperature. The sensor is mounted in the right exhaust manifold before the turbocharger. The sensor's output frequency is 500 Hz with a pulse width that varies with the exhaust temperature. The output signal is referred to as a Duty Cycle or as a Pulse Width Modulated signal. The output signal is expressed as a percentage between 0 and 100 percent. The Cat ET will display the exhaust temperature as a value between 49 °C to 850 °C (120 °F to 1562 °F). If the actual temperature is between −40 °C to 49 °C (−40 °F to 120 °F), the display will read 30 °C (86 °F). If the temperature is above 851 °C (1564 °F), the display will read 851 °C (1564 °F).

Throttle Position Sensor - The Throttle Position Sensor is used to provide a throttle signal to the ECM. The sensor output is a constant frequency signal with a pulse width modulated output that is proportional to rotational input. This output signal is referred to as the Pulse Width Modulated signal (PWM). The sensor will produce a duty cycle of 5 percent to 10 percent at low idle and 90 percent to 95 percent at high idle. The percent duty cycle is translated in the ECM into the throttle position of 0 percent to 100 percent.

Note: Dealers and/or customers can monitor warnings, derates, shutdown override setpoints, and delay times using the Cat ET. Customized parameters may affect the behavior of the ECM. The behavior of the ECM may vary from the description that is given in this System Operation section.

Illustration 1	g00784488
Typical schematic

Test Step 1. Check for Connector Damage.

1. Turn the breaker at the battery to the OFF position.

2. Turn the keyswitch to the OFF position.

3. 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.

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

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

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

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

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring should not have corrosion, abrasion or pinch points.

Results:

• OK - The connectors and wiring are okay. Proceed to Test Step 2.

• Not OK - The connectors and/or wiring are not okay.

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

  STOP

Test Step 2. Check for a Short Circuit in the Wiring Harness.

Note: The circuit for the front engine begins with the letter T. The circuit for the rear engine begins with the letter R. The circuit for the master ECM begins with the letter X.

1. Disconnect ECM connector J1/P1 and all of the digital sensors if you are troubleshooting the digital supply for an exhaust temperature sensor. Disconnect the Master ECM connector J1/P1 and J2/P2 if you are troubleshooting the digital supply for the throttle position sensor.

2. Measure the resistance between the digital supply P1-35 (800-OR(Orange)) and the digital return P1-29 (998-BR(Brown)) on connector P1 if you are troubleshooting the digital supply for an exhaust temperature sensor. Measure the resistance between the digital supply P2-35 (X800-OR(Orange)) and the digital return P1-29 (X998-BR(Brown)) if you are troubleshooting the digital supply for the throttle position sensor.

3. Measure the resistance between the digital supply P1-35 (800-OR(Orange)) and the engine ground if you are troubleshooting the digital supply for an exhaust temperature sensor. Measure the resistance between the digital supply P2-35 (X800-OR(Orange)) and the engine ground if you are troubleshooting the digital supply for the throttle position sensor.

4. Measure the resistance between the digital return P1-29 (998-BR(Brown)) and the engine 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. Proceed to Test Step 3.

• Not OK - The resistance is less than 20,000 Ohms.

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

  STOP

Test Step 3. Check the Digital Supply Voltage at the ECM.

Note: The circuit for the front engine begins with the letter T. The circuit for the rear engine begins with the letter R. The circuit for the master ECM begins with the letter X.

1. Remove the wire P1-35 (800-OR(Orange)) from the harness side of ECM connector P1 if you are troubleshooting the digital supply for an exhaust temperature sensor. Install a wire jumper with a socket on one end into P1-35. Remove the wire P2-35 (X800-OR(Orange)) from the harness side of ECM connector P2 if you are troubleshooting the digital supply for the throttle position sensor. Install a wire jumper with a socket on one end into P2-35.

2. Remove the wire P1-29 (998-BR(Brown)) from the harness side of ECM connector P1. Install a wire jumper with a socket on one end into P1-29.

   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 codes when you are finished.

3. Reconnect ECM connector J1/P1 if you are troubleshooting the digital supply for an exhaust temperature sensor. Reconnect the Master ECM connector J1/P1 and J2/P2 if you are troubleshooting the digital supply for the throttle position sensor.

4. Turn the breaker at the battery to the ON position.

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

6. Measure the voltage between the jumper in P1-35 and the jumper in P1-29 if you are troubleshooting the digital supply for an exhaust temperature sensor. Measure the voltage between the jumper in P2-35 and the jumper in P1-29 if you are troubleshooting the digital supply for the throttle position sensor.

7. Turn the keyswitch to the OFF position.

8. Remove the wire jumpers and reconnect all wires. Reconnect ECM connector J1/P1 and ECM connector J2/P2, if necessary.

Expected Result:

The supply voltage should be 8.0 ± 0.4 VDC.

Results:

• OK - The supply voltage is 8.0 ± 0.4 VDC. The digital sensor supply is producing the correct voltage. Proceed to Test Step 4.

• Not OK - The supply voltage is not 8.0 ± 0.4 VDC. The digital sensor is not producing the correct voltage.

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

  STOP

Test Step 4. Check the Digital Sensor Supply Voltage at the Sensor Connector.

Note: The circuit for the front engine begins with the letter T. The circuit for the rear engine begins with the letter R. The circuit for the master ECM begins with the letter X.

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

2. Measure the digital sensor supply voltage between the digital supply terminal-A (800-OR(Orange)) and the digital return terminal-B (998-BR(Brown)) of all the digital sensors.

   Note: If the sensor is disconnected from the harness, an open circuit diagnostic code will be generated for that sensor. Troubleshoot the original code. Delete the logged diagnostic codes when you are finished.

3. Turn the keyswitch to the OFF position.

Expected Result:

The supply voltage should be 8.0 ± 0.4 VDC.

Results:

• OK - The supply voltage is 8.0 ± 0.4 VDC at all of the digital sensor connectors. Proceed to Test Step 5.

• Not OK - The supply voltage is not 8.0 ± 0.4 VDC. There is an open circuit in the harness or connectors.

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

  STOP

Test Step 5. Check the Digital Sensors for Short Circuits.

Note: The circuit for the front engine begins with the letter T. The circuit for the rear engine begins with the letter R. The circuit for the master ECM begins with the letter X.

1. Connect a voltmeter between terminal-A (800-OR(Orange)) and the digital return terminal-B (998-BR(Brown)) at one of the sensor connectors.

2. Turn the keyswitch to the ON position. The engine should be off.

   Note: If the sensor is disconnected from the harness, an open circuit diagnostic code will be generated for that sensor. Troubleshoot the original code. Delete the logged diagnostic codes when you are finished.

3. Connect one digital sensor at a time.

4. Monitor the voltage reading on the voltmeter as each sensor is connected. Move the voltmeter to another sensor connector in order to check that sensor.

5. Turn the keyswitch to the OFF position.

6. Remove the voltmeter and reconnect all sensors.

Expected Result:

The supply voltage should be 8.0 ± 0.4 VDC.

Results:

• OK - The supply voltage is 8.0 ± 0.4 VDC. The digital sensor supply is correct. The harness and sensors are okay. The problem may be intermittent.

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

  STOP

• Not OK - The supply voltage is not 8.0 ± 0.4 VDC after you connect a sensor. The sensor may be internally shorted.

  Repair: Temporarily install a new sensor. Ensure that the problem is no longer present. Reinstall the old sensor. If the problem returns, replace the sensor.

  STOP