3408E and 3412E Industrial Engines Caterpillar

The digital sensor supply provides power to the auxiliary temperature sensor. The ECM supplies the digital sensor with 8.0 ± 0.5 VDC.

The digital sensor supply is output short circuit protected. This means that the ECM is protected if there is a short circuit to the negative battery or to the positive battery. The digital sensor is NOT protected.

Illustration 1	g00825588
Schematic

Illustration 2	g00894666
P1 ECM connector

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the keyswitch to the OFF/RESET position.

2. Thoroughly inspect the J1/P1 ECM connector, the J2/P2 ECM connector, the J3/P3 customer connector, and all other connectors in the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

Expected Result:

All connectors, pins, and sockets should be completely inserted and coupled. The harness and wiring should be free of corrosion, abrasion, and pinch points. All connections and grounds should be tight and free of corrosion.

Results:

• OK - Proceed to Test Step 2.

• Not OK -

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

  Stop.

Test Step 2. Check for Shorts in the Harness from the ECM to the Digital Sensors

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

2. Measure the resistance between P1:35 (Digital Sensor +8 VDC) and engine ground.

3. Measure the resistance between P1:35 (Digital Sensor +8 VDC) and P1:29 (Digital Sensor Return).

4. Measure the resistance between P1:35 (Digital Sensor +8 VDC) and P1:30 (Analog Sensor Return).

Expected Result:

The resistance should be greater than 20,000 Ohms for each measurement.

Results:

• OK - Proceed to Test Step 3.

• Not OK - There is a short between the ECM and the sensor.

  Repair: Repair the circuit.

  Stop.

Test Step 3. Check for Open Circuits in the Harness Between the ECM and the Digital Sensors

1. Turn the keyswitch to the OFF/RESET position and install a 7X-1715 Adapter Cable (40 Pin Breakout T) at the J1/P1 ECM connector.

2. Use a suitable piece of wire to short P1:35 (Digital Sensor +8 VDC) and P1:29 (Digital Return) at the breakout.

3. Disconnect all of the digital sensors.

4. Measure the resistance between terminal A (+8 VDC) and terminal B (Ground) of the connector for the auxiliary temperature sensor.

5. Remove the wire short from P1:29 of the breakout and insert the wire into P1:30 of the breakout.

6. Measure the resistance between terminal A (+8 VDC) and terminal B (Ground) of the connector for the coolant level sensor.

7. Remove the wire short from the breakout.

Expected Result:

The resistance should be less than 10 Ohms for each measurement.

Results:

• OK - Proceed to Test Step 4.

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

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

  Stop.

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

1. Disconnect all of the digital sensors.

2. Turn the keyswitch to the ON position.

3. Measure the voltage across terminal A (+8 VDC) and terminal B (Ground) of the connector for each digital sensor.

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 5.

• Not OK - The supply voltage is not reaching the sensor. Proceed to Test Step 7.

Test Step 5. Check the Digital Sensor for an Internal Short

1. Disconnect all of the digital sensors.

2. Turn the keyswitch to the ON position.

3. Reconnect the auxiliary temperature sensor while you observe the voltage across P1:35 (Digital Sensor +8 VDC) and P1:29 (Digital Sensor Return) at the breakout.

4. Reconnect the coolant level sensor while you observe the voltage across P1:35 (Digital Sensor +8 VDC) and P1:30 (Analog Sensor Return) at the breakout.

Expected Result:

The supply voltage should be 8.0 ± 0.5 VDC. The voltage should not drop when the sensors are connected.

Results:

• OK - The sensor does not have an internal short.

  Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.

  Stop.

• Not OK - The sensor may have an internal short. Proceed to Test Step 6.

Test Step 6. Temporarily Install a New Sensor

1. Remove the suspect sensor.

2. Temporarily install a new sensor.

3. Turn the keyswitch to the ON position.

4. Observe the voltage across P1:35 (Digital Sensor +8 VDC) and P1:29 (Digital Sensor Return) at the breakout while you connect the auxiliary temperature sensor.

5. Observe the voltage across P1:35 (Digital Sensor +8 VDC) and P1:30 (Analog Sensor Return) at the breakout while you connect the coolant level sensor.

Expected Result:

The supply voltage should be 8.0 ± 0.5 VDC. The voltage should not drop when the sensor is connected.

Results:

• OK - The suspect sensor was faulty.

  Repair: Permanently install the new sensor.

  Stop.

• Not OK - The sensor and the circuit appear to be OK at this time.

  Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.

  Stop.

Test Step 7. Check the Digital Sensor Supply Voltage at the ECM

1. Disconnect all of the digital sensors.

2. Turn the keyswitch to the ON position.

3. Measure the voltage across P1:35 (Digital Sensor +8 VDC) and P1:29 (Digital Sensor Return) at the breakout.

4. Measure the voltage across P1:35 (Digital Sensor +8 VDC) and P1:30 (Analog Sensor Return) at the breakout.

Expected Result:

The supply voltage should be 8.0 ± 0.5 VDC.

Results:

• OK - The ECM is supplying the correct voltage.

  Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.

  Stop.

• Not OK - The ECM is not supplying the correct voltage.

  Repair: Verify your results.Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.Verify that the repair eliminates the problem.

  Stop.