3500B Series II Marine Engines Caterpillar

The digital sensor supply provides power to all of the digital sensors on the engine. The Electronic Control Module (ECM) supplies 8.0 ± 0.4 VDC from the ECM connectors J1/P1 and J2/P2 to each digital sensor connector pin "A". The digital sensor reference is used as the return line for the digital sensors, speed/timing sensors, and the switch inputs to the ECM. The digital reference line is from the ECM connector J1/P1 and J2/P2 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).

Illustration 1	g01017251
Typical example

Test Step 1. Check for Connector Damage

1. Turn the Engine Control Switch (ECS) to the OFF/RESET position.

2. Turn the battery disconnect switch 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 allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the correct torque values.

6. 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 are free of corrosion, of abrasion, and of pinch points.

Results:

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

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

  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

1. Disconnect the ECM connector J1/P1 and ECM connector J2/P2. Disconnect all of the digital sensors.

2. Measure the resistance between the digital supply wire 700 in P1-4 and the digital return wire D998 in P1-5 of connector P1.

3. Measure the resistance between the digital supply wire 700 in P1-4 and engine ground.

4. Measure the resistance between the digital return wire D998 in P1-5 and engine ground.

5. Measure the resistance between the digital supply wire 700 in P1-4 and the +Battery terminal.

6. Measure the resistance between the digital return wire D998 in P1-5 and the +Battery terminal.

7. Measure the resistance between the digital supply P2-56 (A700-BK(Black)) and the digital return P2-66 (F998-BK(Black)) on connector P2.

8. Measure the resistance between the digital supply wire A700 in P2-56 and engine ground.

9. Measure the resistance between the digital return wire F998 in P2-66 and engine ground.

10. Measure the resistance between the digital supply wire A700 in P2-56 and the +Battery terminal.

11. Measure the resistance between the digital return wire F998 in P2-66 and the +Battery terminal.

Expected Result:

The resistance is 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: There is a short in the wiring harness. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

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

1. Remove the wire 700 from the ECM connector P1-4. Install a jumper wire into the socket for P1-4.

2. Remove the wire D998 from the ECM connector P1-5. Install a jumper wire into the socket for P1-5.

3. Remove the wire A700 from the ECM connector P1-4. Install a jumper wire into the socket for P2-56.

4. Remove the wire F998 from the ECM connector P2-66. Install a jumper wire into the socket for P2-66.

   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.

5. Turn the battery disconnect switch to the ON position.

6. Turn the ECS to the STOP position. The engine should be off.

7. Measure the voltage between the digital sensor supply P1-4 and the digital sensor return P1-5 at the wire jumpers.

8. Measure the voltage between the digital sensor supply P2-56 and the digital sensor return P2-66 at the wire jumpers.

9. Turn the ECS to the OFF/RESET position.

10. Turn the battery disconnect switch to the OFF position.

11. Remove the wire jumpers and reconnect the ECM connector J1/P1.

12. Remove the wire jumpers and reconnect the ECM connector J2/P2.

Expected Result:

The supply voltage is 8.0 ± 0.4 VDC.

Results:

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

• Not OK - The supply voltage is not 8.0 ± 0.4 VDC. The digital sensor supplies are 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

1. Turn the battery disconnect switch to the ON position.

2. Turn the ECS to the STOP position. The engine should be off.

3. Measure the digital sensor supply voltage between the digital supply wire 700 in terminal-A and the digital return wire D998 in terminal-B at all of the digital sensors.

4. Measure the digital sensor supply voltage between the digital supply wire A700 in terminal-A and the digital return wire F998 in terminal-B at all of 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.

5. Turn the ECS to the OFF/RESET position.

6. Turn the battery disconnect switch to the OFF position.

Expected Result:

The supply voltage is 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

1. Turn the battery disconnect switch to the ON position.

2. Turn the ECS to the STOP 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. Measure the voltage between the digital sensor supply P1-4 and the digital sensor return P1-5 at the ECM connector J1/P1. Repeat these steps with all of the digital sensors.

5. Measure the voltage between the digital sensor supply P2-56 and the digital sensor return P2-66 at the ECM connector J2/P2. Repeat these steps with all of the digital sensors.

6. Turn the ECS to the OFF/RESET position.

7. Turn the battery disconnect switch to the OFF position.

Expected Result:

The supply voltage is 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 OK.

  Repair: Check the system for any diagnostic codes.

  STOP

• Not OK - The supply voltage is not 8.0 ± 0.4 VDC. 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

• Intermittent - The problem is intermittent.

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

  STOP