G3516 TA Engine 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.
974-5 Remote Accelerator Pedal Position : Current Below Normal	The ECM has detected a low current in the circuit for the "4-20 mA" desired speed signal. The current is less than 2 mA for more than 5 seconds. The code is logged. The alarm output is activated.
974-6 Remote Accelerator Pedal Position : Current Above Normal	The ECM has detected an excessive current in the circuit for the "4-20 mA" desired speed signal. The current has exceeded 22 mA for more than 5 seconds. The code is logged. The alarm output is activated.

For this troubleshooting procedure, the "Desired Speed Input" configuration parameter can be set to "4 - 20 mA" input, "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 OCP panel and either the 0-5 Volt analog output or the PWM speed control feature, then the OCP panel 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 OCP panel 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".

When the idle/rated speed switch is in the IDLE position, a current value of 4.0 mA, 5% duty cycle, or .5 Volts corresponds to the programmed "Minimum Engine High Idle Speed". A current value of 20.0 mA, 95% duty cycle, or 4.5 Volts corresponds to "Maximum Engine High Idle Speed". Desired speed input values within this range will vary the desired engine speed in a linear fashion between. The range will vary between "Minimum Engine High Idle Speed" and "Maximum Engine High Idle Speed".

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	g06116337
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 and pinch points.	Connectors and Wiring	Result: The connectors and wiring appear to be OK. Proceed to Test Step 2. Result: There is a problem with the connectors and/or wiring. Repair: Repair or replace the connectors or wiring. Ensure that all the seals are properly in place and ensure that the connectors are coupled. If the problem is not resolved, proceed to Test Step 2.
2. Check for Codes A. Connect Cat® Electronic Technician (ET) to the service tool connector. B. Determine if a code is active or logged.	Codes	Result: Any of the following codes are active or logged: - 29-4 - 91-4 - 91-8 Proceed to Test Step 3. Result: Any of the following codes are active or logged: - 29-3 - 91-3 - 974-6 Proceed to Test Step 7. Result: A 974–5 code is active or logged: Proceed to Test Step 9.
3. Check the Wiring for an Open Circuit A. Ensure that the engine control is in the OFF/RESET position. Ensure that the electrical power is removed from the engine and the speed control device. B. Remove the signal wire at the Engine Interface Connector (EIC), that carries the (PWM or analog 0-5 Volt) desired speed input signal to the engine ECM. Refer to Illustration 1. C. Perform one of the following: - For the 91-4 and 91-8 disconnect the A-C1 connector from the ECM. - For the 29-4 diagnostic disconnect the A-C2 connector from the ECM. D. Measure the resistance between the following terminals at the removed ECM connector: - For the 91-4 and 91-8 codes, terminal 66 of the A-C1 ECM connector and terminal 66 of the A-C9 connector. - For the 29-4 code, terminal 94 of the A-C2 ECM connector and terminal 15 of the A-C9 connector. Refer to Illustration 1.	Open Circuit	Result: The resistance measured less than 10 ohms. Proceed to Test Step 4. Result: The resistance measured more than 10 ohms. Repair: An open circuit has been detected. Repair or replace the wiring harness.
4. Check the Wiring for a Short Circuit to Engine Ground A. Measure the resistance between the ground strap for the ECM and the following terminals at the ECM connector. - For the 91-4 and 91-8 codes terminal 66 of the A-C1 ECM connector. - For the 29-4 code, terminal 94 of the A-C2 ECM connector Refer to Illustration 1.	Short Circuit	Results: The resistance measured more than 100k ohms. The signal wire is not shorted to the engine ground. Proceed to Test Step 5. Results: The resistance measured less than 100k ohms. The signal wire is shorted to the engine ground. Repair: Repair or replace the wiring harness.
5. Check the Wiring Harness for a Pin to Pin Short Circuit A. Turn the main disconnect switch to the OFF position. B. Disconnect the wiring harness from the ECM. C. Measure the resistance between the following ECM connector terminals: - For the 91-4 and 91-8 codes, terminal 66 of the A-C1 ECM connector and all other terminal in the ECM connector. - For the 29-4 code, terminal 94 of the A-C2 ECM connector and all other terminal in the ECM connector. Refer to Illustration 1.	Short Circuit	Results: One or more of the measurements were less than 100 K ohms between the affected signal wire terminal and any other terminal in the ECM connector. There is a short circuit in the wiring harness. Repair: Repair or replace the wiring harness. Results: All measurements were greater than 100 K ohms between the affected signal wire terminal and all other terminals in the ECM connector. There is not a short circuit in the wiring harness. Proceed to Test Step 6.
6. Check the Device that Provides the Desired Engine Speed Signal A. Measure the desired engine speed signal, according to the literature that is provided by the OEM of the device. B. Verify that the correct signal is being provided from the device as close to the device as possible. C. Verify that the correct signal is present at the correct EIC terminal. - For the 91-4 and 91-8 codes, EIC terminal 66. - For the 29-4 code, EIC terminal 15. Refer to Illustration 1.	Desired Speed Signal	Results: The speed control device is not providing the correct desired speed input signal. Repair: Service the device that is providing the desired engine speed signal, according to the literature that is provided by the OEM of the device. Results: The speed control device is providing the correct desired speed input signal and the signal measured at the EIC is not correct. Repair: There is an open circuit or short to ground with the wiring in between the speed control device and the EIC. Refer to Customer system schematics or instruction for additional information. Verify that the repair eliminated the problem.
7. Check the Wiring Between the ECM and the Speed Control Device for a Short Circuit to the +Battery or Ground A. Turn the battery disconnect to the OFF position. B. Remove the wires for the desired speed from the speed control device. D. Turn the battery disconnect switch to the ON position. E. Observe Cat ET for a diagnostic FMI state change.	Short Circuit	Results: The -3 or -6 code remains active after the signal wire is removed from the speed control device providing the desired speed signal. A -3 code indicates a short to a positive voltage. A -6 code indicates a short to ground. Proceed to Test Step 8. Results: The -3 or -6 code is no longer active and has transitioned to logged. A -4 or -5 code is now active. Repair: Service the device that is providing the desired engine speed signal, according to the literature that is provided by the OEM of the device.
8. Check the Wiring Between the ECM and the EIC for a Short Circuit to the +Battery or Ground A. Turn the battery disconnect to the OFF position. B. Remove the wire for desired speed signal from the EIC - For the 91-3 code, EIC terminal 66. - For the 29-3 code, EIC terminal 15. - For the 974-6 code, EIC terminal 10. C. Turn the battery disconnect to the ON position.	Short Circuit	Results: The -3 or -6 code remains active after the signal wire is removed from the EIC. The signal wire between the A-C9 connector and ECM is shorted. A -3 code indicates a short to a positive voltage. A -6 code indicates a short to ground. Repair: Repair or replace the wiring harness between the A-C9 connector and the ECM. Results: The-3 or -6 code is no longer active after the signal wire is removed from the EIC. The signal wire between the EIC and the speed control device is shorted. A -3 code indicates a short to a positive voltage. A -6 code indicates a short to ground. Repair: Repair or replace the wiring harness between the EIC and the speed control device.
9. Check the Wiring Between the ECM and the Speed Control Device for an Open Circuit. A. Turn the battery disconnect to the OFF position. B. Remove the connector for the desired speed from the speed control device. C. Install a jumper wire between the 4-20 mA (+) and (-) terminals to create a short circuit. D. Turn the battery disconnect to the ON position. E. Observe Cat ET for a diagnostic FMI state change.	Short Circuit	Results: The -5 code remains active after the short circuit was created between the 4-20 mA (+) and (-) at the connector for the speed control device. An open circuit is present in the wiring between the ECM and the speed control device. Proceed to Test Step 10. Results: The -5 code is no longer active and has transitioned to logged. A -6 code is now active. Repair: Service the device that is providing the desired engine speed signal, according to the literature that is provided by the OEM of the device.
10. Check the Wiring Between the ECM and the EIC for an Open Circuit. A. Turn the battery disconnect to the OFF position. B. Remove the wires for the 4-20 mA (+) and (-) from the EIC Refer to Illustration 1. C. Short the circuit to the ECM by replacing the removed wires with a jumper. D. Turn the battery disconnect to the ON position.	Short Circuit	Results: The -5 code remains active after the short circuit was created. An open circuit is present in the wiring between the ECM and the A-C9 connector. Repair: Repair or replace the wiring harness between the A-C9 connector and the ECM. Results: The -5 code is no longer active and has transitioned to logged, after the short circuit was created. A -6 code is now active. Repair: Repair or replace the wiring harness between the EIC and the speed control device.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).