C11 and C13 Engines for Caterpillar Built Machines Throttle Switch Circuit - Test Caterpillar

System Operation Description:

This procedure covers the following diagnostic codes:

• 91-08 Throttle Position signal abnormal

The throttle switch provides the operator with the ability to select the desired engine speed. The throttle switch is a rotary switch with ten positions. The throttle switch is connected to the four switch inputs of the engine and hydraulic pump controller. A throttle command is sent to the engine's Electronic Control Module (ECM) from the engine and hydraulic pump controller. The throttle command is referred to as a duty cycle or as a PWM signal. The throttle command is valid when the following conditions exist:

• The duty cycle is between 5 percent and 95 percent.

• The PWM signal is 1.228 kHz ± 150 Hz.

When a diagnostic code is generated, the ECM ignores the throttle command and the desired engine speed is set to the last valid speed that was recognized by the ECM. When a problem is detected with the throttle signal, the throttle backup switch is enabled. The operator can use the throttle backup switch to set the desired engine speed. If the throttle backup switch is held in the ACCEL position, the desired engine speed will increase 200 rpm per second. If the throttle backup switch is held in the DECEL position, the engine speed will decrease 200 rpm per second.

Illustration 1	g01253310
Schematic

Table 1 shows continuity between the contacts of the throttle position switch in each position.

Illustration 2	g01120703
P1 ECM connector (P1-5) Digital return (P1-22) Throttle backup switch (P1-23) Throttle backup switch (P1-66) Throttle command

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the J1/P1 ECM connector and the J2/P2 ECM connector. Inspect all of the connectors that are associated with the circuit.

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that is associated with the active diagnostic code.

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

5. Check the harness and wiring for abrasions and for pinch points from the sensors back to the ECM.

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 harness 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 for Active Diagnostic Codes

1. Connect AVSpare Electronic Technician (ET) to the service tool connector.

2. Turn the keyswitch to the ON position.

3. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active.

  Repair: The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - A 91-08 diagnostic code is active at this time. Proceed to Test Step 3.

Test Step 3. Check the Throttle Signal on Cat ET

1. Turn the keyswitch to the ON position.

2. Observe the status of "Throttle" on Cat ET.

3. Turn the throttle switch and observe the status of "Throttle" on Cat ET.

4. Turn the keyswitch to the OFF position.

Expected Result:

The throttle varies from 0 to 100 percent.

Results:

• OK - The throttle varies from 0 to 100 percent. The throttle and circuitry are operating correctly.

  Repair: If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The throttle signal did not vary from 0 to 100 percent. Proceed to Test Step 4.

Test Step 4. Check the Throttle Command at the Engine and Hydraulic Pump Controller

1. Remove the wire F889-WH(White) from terminal 44 of the engine and hydraulic pump controller.

2. Turn the keyswitch to the ON position.

3. Use a multimeter to monitor the percent duty cycle of the throttle command at terminal 44 of the engine and hydraulic pump controller. Adjust the throttle switch from the low idle position to the high idle position.

4. Turn the keyswitch to the OFF position.

Expected Result:

At low idle, the duty cycle is between 5 percent and 10 percent. At high idle, the duty cycle is between 90 percent and 95 percent.

Results:

• OK - The throttle command is correct. Proceed to Test Step 5.

• Not OK - The throttle command is not correct. There may be a problem with the throttle switch or the engine and hydraulic pump controller.

  Repair: If a problem is suspected with the throttle position switch, refer to Table 1 for information on continuity between the switch contacts when the switch is in each position.

  If a problem is suspected with the engine and hydraulic pump controller, refer to the System Operation manual and the Testing and Adjusting manual for the machine.

  STOP

Test Step 5. Check the Throttle Command at the ECM

1. Turn the keyswitch to the OFF position.

2. Fabricate a jumper wire that can be used to replace the signal wire in the ECM connector for the throttle signal. Crimp a connector socket to one end of the jumper wire.

3. Disconnect the J1/P1 ECM connector.

4. Remove the wire F889-WH(White) from ECM connector P1-66. Install the jumper wire into the terminal location for the throttle signal at the ECM connector.

5. Reconnect the ECM connectors.

6. Turn the keyswitch to the ON position.

7. Use a multimeter to monitor the percent duty cycle of the throttle command between ECM connector P1-66 (throttle command) and engine ground. Adjust the throttle switch from the low idle position to the high idle position.

8. Turn the keyswitch to the OFF position.

9. Replace all wires to the original configuration.

Expected Result:

At low idle, the duty cycle is between 5 percent and 10 percent. At high idle, the duty cycle is between 90 percent and 95 percent.

Results:

• OK - The throttle command is correct. The ECM is not processing the command properly. Verify that the ECM is receiving the correct battery voltage. If the ECM is receiving the correct battery voltage, replace the ECM.

  Repair: Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.

  STOP

• Not OK - The throttle command is not correct.

  Repair: There is a problem in the harness or connectors between the engine and hydraulic pump control and the ECM. Repair the circuit. Verify that the repair eliminates the problem.

  STOP