CUP 8S2125 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the circuit that is for the throttle position sensor. Also use this procedure if one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
J1939 Code and Description Comments
29-3
Accelerator Pedal Position #2 : Voltage Above Normal The Electronic Control Module (ECM) has detected that the analog "0-5 Volt" desired speed signal has exceeded the 4.5 volt trip point.
The setting for the upper diagnostic limit has been exceeded for .6 seconds.
The code is logged.
29-4
Accelerator Pedal Position #2 : Voltage Below Normal The ECM has detected that the analog "0-5 Volt" desired speed signal is below the .5 volt trip point.
The setting for the lower diagnostic limit has been exceeded for .6 seconds.
The code is logged.
91-3
Accelerator Pedal Position #1 : Voltage Above Normal The ECM has detected that the "PWM" desired speed signal is above the 95% diagnostic limit.
The code is logged.
The alarm output is activated.
91-4
Accelerator Pedal Position #1 : Voltage Below Normal The ECM has detected that the "PWM" desired speed signal is below the 5% diagnostic limit.
The code is logged.
The alarm output is activated.
91-8
Accelerator Pedal Position #1 : Abnormal Frequency, Pulse Width, or Period The ECM has detected an erratic signal for the "PWM" desired speed signal.
The code is logged.
The alarm output is activated. For this troubleshooting procedure, the "Desired Speed Input" configuration parameter can be set to "PWM" input or "0-5 Volt" input.The engine ECM will only monitor the status of the input signal for the PWM and 0-5 Volt desired speed inputs.The engine ECM does not supply the power and ground for the PWM or 0-5 Volt speed control circuits.If using the EMCP 4.3 and either the 0-5 Volt analog output or the PWM speed control feature, then the EMCP 4.3 will monitor the status of those outputs in relation to power and ground circuit health.If an external speed control source device is used, refer to that devices troubleshooting procedure.If using the EMCP 4.3 CAN desired speed input, refer to Troubleshooting, "Data Link - Test".The value of the current, frequency, or voltage corresponds to a range of desired engine speeds between minimum high idle and maximum high idle. The "Minimum Engine High Idle Speed" and the "Maximum Engine High Idle Speed" are set with the "Service/Configuration" screen of Cat ET. For more information, refer to Troubleshooting, "Configuration Parameters".The most likely causes of a diagnostic code for this circuit are a poor connection or a problem in a wiring harness. The next likely cause is a problem with a component. The least likely cause is a problem with the ECM.
Illustration 1 g06189909
For the complete circuit details, refer to the full schematic.
Table 2
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Turn the main disconnect switch to the OFF position.
B. Thoroughly inspect the connectors. Refer to Troubleshooting, "Electrical Connectors-Inspect" for additional information.
C. Perform a 45 N (10 lb) pull test on the connector wires.
D. Check the harness for abrasions