3512C and 3516C Engines Caterpillar

Use this procedure in order to troubleshoot the electrical system if a problem is suspected with the throttle signal. Use this procedure if the diagnostic code in Table 1 is active or easily repeated.

Terminal BN on the customer connector provides the throttle signal to the engine's ECM. The throttle signal should be a 500 Hz constant frequency signal with a pulse width that varies with the throttle signal. This output signal is referred to as a Pulse Width Modulated signal (PWM). This signal is expressed as a percentage between 0 percent and 100 percent.

The throttle signal's duty cycle should be between 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: The ECM will not respond to the throttle signal if there is an active 253-02 Personality Module erratic, intermittent, or incorrect.

Illustration 1	g01194084

Illustration 2	g00725481
Throttle Position Versus PWM Input

Illustration 3	g01242355
P1 ECM connector (P1-10) Throttle signal

Illustration 4	g01242356
Customer connector (Terminal BN) Throttle signal

Illustration 5	g01234146
Location of ECM connectors

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the ECS to the OFF position.

2. Thoroughly inspect the ECM connectors. Inspect all of the other connectors for the circuit. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

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

4. Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.

5. 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 - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.

  Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Throttle Position on Caterpillar Electronic Technician (ET)

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

2. Observe the position of the throttle on Cat ET.

3. Adjust the speed control to the lowest setting.

4. Start at the lowest position. Slowly adjust the speed control to the highest setting. Monitor the position of the throttle on Cat ET.

Expected Result:

The throttle position on Cat ET is 0 percent at the lowest setting and 0 to 100 percent as the speed control is adjusted to the highest setting.

Results:

• OK - The speed control is operating correctly.

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

  STOP

• Not OK - The throttle position on Cat ET does not change correctly. Proceed to Test Step 3.

Test Step 3. Check the Duty Cycle at the Customer Connector

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

2. Remove wire F702-BK(Black) for the throttle signal from the customer connector on terminal BN.

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

4. Place the red probe of the digital multimeter on terminal BN of the customer connector. Place the black probe of the multimeter on the −Battery terminal.

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

6. Measure the percent duty cycle of the throttle signal. Adjust the speed control from the lowest position to the highest position.

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

8. Replace all connectors and wires.

Expected Result:

The duty cycle is 5 to 10 percent at the lowest setting. The duty cycle is 90 to 95 percent at the highest setting.

Results:

• OK - The duty cycle is correct. Proceed to Test Step 4.

• Not OK - The duty cycle reading is not correct. The throttle position signal is not reaching the customer connector.

  Repair: Check the signal from the customer connector to the speed control.

  STOP

Test Step 4. Check the Duty Cycle at the ECM Connector

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

2. Remove the ECM connector P1 from the ECM. Remove the throttle signal wire F702-BK(Black) from the ECM connector P1-10.

3. Reconnect the ECM connector J1/P1.

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

5. Place the red probe of the multimeter on wire F702-BK(Black) that was removed from P1-10 of the ECM connector P1. Place the black probe of the multimeter on the −Battery terminal.

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

7. Measure the percent duty cycle of the throttle signal. Move the speed control from the lowest setting to the highest setting.

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

9. Replace all connectors and wires.

Expected Result:

The duty cycle is 5 to 10 percent at the lowest setting. The duty cycle is 90 to 95 percent at the highest setting.

Results:

• OK - The duty cycle is correct.

  Repair: The throttle position signal is reaching the ECM. Reconnect all wiring and verify that the ECM is not reading the throttle position signal. If the ECM does not read the throttle position signal, replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP

• Not OK - The duty cycle reading is not correct. The throttle signal is not reaching the ECM.

  Repair: Repair the wire F702-BK(Black) between ECM connector P1-10 and the customer connector BN.

  STOP