C7.1 Engines and Generator Sets Caterpillar

Switch Circuits - Test - Multiposition Throttle Switch

Usage:

C7.1 770

This procedure covers the following diagnostic codes:

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Table 1
Diagnostic Trouble Codes for Throttle Switch
J1939 Code	CDL Code	Code Description (code descriptions may vary)	Comments
29-2	774-2	Accelerator Pedal Position 2 : Erratic, Intermittent or Incorrect	The Electronic Control Module (ECM) detects the following condition: There is an invalid combination of positions for the multi-position switch. If equipped, the warning light will come on. The ECM will log the diagnostic code.
91-2	91-2	Accelerator Pedal Position 1 : Erratic, Intermittent or Incorrect
Follow the troubleshooting procedure to identify the root cause of the fault.

If the application is equipped with two throttles, the engine will use the second throttle until the fault is repaired.

If a second throttle is not installed or if the second throttle has a fault, the following conditions will occur:

The engine will default to the limp home speed.
If the engine speed is higher than the limp home speed, the engine will decelerate to the limp home speed.
If the engine speed is lower than the limp home speed, the engine speed will remain at the current speed.
The engine will remain at this speed while the diagnostic code remains active.
All inputs from the faulty throttle are ignored by the ECM until the fault is repaired.
All inputs from the repaired throttle will be ignored by the ECM until the keyswitch has been cycled.

Check that the software configuration in the ECM is correct for a multi-position throttle.

If the engine has an analog throttle with an Idle Validation Switch (IVS), then refer to Troubleshooting, "Idle Validation - Test".

The throttle switch provides the operator with the ability to select the desired engine speed. The throttle switch configuration may be selected between 0 to 4 switches. A multi-position rotary switch may be used.

The throttle switch is typically connected to the four throttle inputs of the ECM. Each position generates a specific ON/OFF pattern on the throttle inputs. A diagnostic code is generated if a pattern that does not correspond with any of the switch positions is detected.

Once a diagnostic code is generated, the ECM ignores the throttle input signals. The desired engine speed is set to low idle if no alternative throttle is detected.

Voltage at the throttle inputs to the ECM should be 13.8 ± 0.5 VDC when the throttle inputs are open. The voltage should be less than 0.5 VDC when the throttle inputs are closed.

During the following procedure, refer to the electrical schematic for the application.

Complete the procedure in the order in which the steps are listed.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Inspect Electrical Connectors and Wiring A. Turn the keyswitch to the OFF position. B. Thoroughly inspect the P1 connector and any other connectors that are included in the application for this throttle switch. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Perform a 45 N (10 lb) pull test on each of the wires in the switch connector and the ECM connector that are associated with the active diagnostic code. D. Check the screw for the ECM connector for the correct torque of 6 N·m (53 lb in). E. Check the ground connection on the ECM for abrasions and pinch points. F. Check the harness for abrasion and pinch points from the suspect sensor to the ECM.	Loose connection or damaged wire	Result: There is a fault in a connector or the wiring. Repair: Repair any faulty connectors or replace the wiring harness. Ensure that all the seals are properly in place and ensure that the connectors are correctly coupled. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: All connectors, pins, and sockets are correctly coupled and/or inserted. The harness is free of corrosion, abrasion, and pinch points. Proceed to Test Step 2.
2. Check Throttle Cab Switch Position on the Electronic Service Tool A. Connect the electronic service tool to the diagnostic connector. B. Turn the keyswitch to the ON position. C. Observe the status of the throttle switch and the throttle inputs on the electronic service tool while moving the throttle switch to each position.	Throttle switch status changes on the electronic service tool	Result: The throttle switch is functioning correctly. If there are logged diagnostic codes for the throttle switch, the fault may be intermittent. Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" to identify intermittent faults. Result: Record the suspect input. Proceed to Test Step 3.
3. Install a Jumper at the Throttle Switch Connector A. Disconnect the connector for the throttle switch. B. Observe the status of the suspect throttle input on the electronic service tool. C. Connect a suitable jumper wire between terminal 1 on the throttle switch connector and the terminal for the suspect throttle input. D. Observe the status of the suspect throttle input on the electronic service tool. E. Remove the jumper wire.	Status is ON with jumper installed Status is OFF with jumper removed	Result: The fault is in the throttle switch. Repair: Install a replacement throttle switch. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The fault is not in the throttle switch. Proceed to Test Step 4.
4. Check the Harness for an Open Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the P1 ECM connector and the connector for the throttle switch. C. Measure the resistance between each of the throttle switch inputs and the appropriate terminal on the P1 connector. D. Measure the resistance between the return terminal on the throttle switch and the "Switch Return" terminal on the P1 connector.	Less than 2.0 Ohms	Result: At least one of the resistance measurements is greater than 2.0 Ohms. The fault is in the wiring between the throttle switch and the P1 connector. Repair: Repair the faulty wiring or replace the faulty wiring. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair has eliminated the fault. Result: All resistance measurements are less than 2.0 Ohms. Proceed to Test Step 5.
5. Check the Harness for a Short Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the P1 ECM connector and the connector for the throttle switch. C. Measure the resistance between the suspect input terminal and all other terminals on the P1 connector. D. Measure the resistance between the "Switch Return" terminal and all other terminals on the P1 connector.	Greater than 100 Ohms	Result: At least one of the resistance measurements is less than 100 Ohms. There is a short in the harness between the throttle switch connector and the P1 connector. Repair: Repair the faulty wiring or replace the faulty wiring. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: All resistance measurements are greater than 100 Ohms. Contact the Dealer Solutions Network (DSN).