3126B Engine for Caterpillar Built Machines Digital Sensor Supply Circuit - Test Caterpillar

System Operation Description:

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

The digital sensor supply is output short circuit protected. The ECM is protected from a short to ground and a short to + battery condition. The digital sensor is NOT protected.

Illustration 1	g00807537
Schematic

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 J61/P61 machine connector, and all other connectors in the circuit. 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 Sensor

Illustration 2	g00807533
ECM connector P1

1. Disconnect ECM connector J1/P1 and the digital sensor.

2. Measure the resistance between P1:4 (Digital Sensor +8 VDC) and engine ground.

3. Measure the resistance between P1:4 (Digital Sensor +8 VDC) and P1:5 (Digital Sensor Return).

4. Leave the J1/P1 ECM connector and the digital sensor disconnected.

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 Sensor

Illustration 3	g00807533

Note: The J1/P1 ECM connector and the digital sensor should still be disconnected.

1. Install a jumper wire between P1:4 (Digital Sensor +8 VDC) and P1:5 (Digital Sensor Return).

2. Measure the resistance between terminal A (+8 VDC) and terminal B (Return) of the connector for the digital sensor.

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 Connector

1. Disconnect the digital sensor.

2. Turn the keyswitch to the ON position.

3. Measure the voltage across terminal A (+8 VDC) and terminal B (Return) of the connector for the 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. Install a 7X-6370 Adapter Cable (3 Pin DT Breakout) at the sensor connector, but do not connect the sensor to the breakout at this time.

2. Turn the keyswitch to the ON position.

3. Reconnect the digital sensor while you observe the voltage across terminals A (Digital Sensor +8 VDC) and B (Return) at the breakout.

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 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. Disconnect the suspect sensor and remove the suspect sensor.

2. Turn the keyswitch to the ON position.

3. Temporarily connect a new sensor to the breakout while you observe the voltage across terminals A (Digital Sensor +8 VDC) and B (Return) at the breakout.

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

Illustration 4	g00807533
J1/P1 breakout

1. Install a 140-2266 Adapter Cable (70 Pin Breakout) at the J1/P1 ECM connector.

2. Turn the keyswitch to the ON position.

3. Measure the voltage across P1:4 (Digital Sensor +8 VDC) and P1:5 (Digital 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