C280 Marine Engines Caterpillar

Use this procedure to troubleshoot a problem with the throttle position sensor. Also, use this procedure if one of the following diagnostic codes is active or easily repeated.

Table 1

J1939 Code and Description	CDL Code and Description	Comments
28-3 Accelerator Pedal Position 3 : Voltage Above Normal	774-3 Secondary Throttle Position Sensor : Voltage Above Normal	The Electronic Control Module (ECM) detects signal voltage that is not in the acceptable range. The ECM flags the throttle position as invalid data and a default value is used. The engine speed is limited to high idle. The code is logged.
28-4 Accelerator Pedal Position 3 : Voltage Below Normal	774-4 Secondary Throttle Position Sensor : Voltage Below Normal	The ECM detects signal voltage that is not in the acceptable range. The ECM flags the throttle position as invalid data and a default value is used. The engine speed is limited to high idle. The code is logged.
29-3 Accelerator Pedal Position 2 : Voltage Above Normal	774-3 Secondary Throttle Position Sensor : Voltage Above Normal	The ECM detects signal voltage that is not in the acceptable range. The ECM flags the throttle position as invalid data and a default value is used. The engine speed is limited to high idle. The code is logged.
29-4 Accelerator Pedal Position 2 : Voltage Below Normal	774-4 Secondary Throttle Position Sensor : Voltage Below Normal	The ECM detects signal voltage that is not in the acceptable range. The ECM flags the throttle position as invalid data and a default value is used. The engine speed is limited to high idle. The code is logged.
29-8 Accelerator Pedal Position 2 : Abnormal Frequency, Pulse Width, or Period	774-8 Secondary Throttle Position Sensor : Abnormal Frequency, Pulse Width, or Period	The Pulse Width Modulated (PWM) signal from the sensor to the ECM is not correct. The code is logged.
91-3 Accelerator Pedal Position 1 : Voltage Above Normal	91-3 Throttle Position Sensor : Voltage Above Normal	The ECM detects signal voltage that is not in the acceptable range. The ECM flags the throttle position as invalid data and a default value is used. The engine speed is limited to high idle. The code is logged.
91-4 Accelerator Pedal Position 1 : Voltage Below Normal	91-4 Throttle Position Sensor : Voltage Below Normal	The ECM detects signal voltage that is not in the acceptable range. The ECM flags the throttle position as invalid data and a default value is used. The engine speed is limited to high idle. The code is logged.
91-8 Accelerator Pedal Position 1 : Abnormal Frequency, Pulse Width, or Period	91-8 Throttle Position Sensor : Abnormal Frequency, Pulse Width, or Period	The PWM signal from the sensor to the ECM is not correct. The code is logged.

Note: Performing steps within this procedure requires the use of a multimeter capable of measuring a PWM duty cycle and frequency. Refer to Table 2 for the tools recommended for the procedure.

Table 2

Recommended Tools

146-4080 Digital Multimeter Gp

7X-1710 Multimeter Probe

326-4904 Adapter Cable As

Table 3

Troubleshooting Test Steps	Values	Results
1. 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: A 28-5 or 1923-5 code is active or logged. Proceed to Test Step 4. Result: A 28-6 or 1923-6 code is active or logged. Proceed to Test Step 5. Result: A 29 or 91 code is active or logged. Proceed to Test Step 2.
2. Check the Signal Frequency and the Duty Cycle at the Sensor A. Turn the keyswitch to the OFF position. B. Remove the wire from terminal location C (Throttle position) on the wiring harness side of the connector for the throttle position sensor. C. Install a 326-4904 Adapter Cable As (3-PIN BREAKOUT) at the connector for the throttle position sensor. D. Connect the connector for the throttle position sensor. E. Turn the keyswitch to the ON position. F. Measure the frequency and the duty cycle at the 326-4904 Adapter Cable As (3-PIN BREAKOUT) between the following terminals: - B (Digital return) and C (Throttle position) G. Operate the throttle pedal while making the measurements. H. Turn the keyswitch to the OFF position. J. Remove the breakout harness. K. Restore the wiring harness connector to the original configuration.	Frequency Duty cycle	Result: The ECM detects an incorrect frequency on the throttle signal or an incorrect duty cycle on the throttle signal. The frequency is below 150 Hz or the frequency is above 1000 Hz. The duty cycle is less than 5 percent or the duty cycle is greater than 95 percent. Proceed to Test Step 3. Result: The frequency and the duty cycle are within specifications for the entire range of the pedal. Repair: Repair or replace the wiring harness. If the problem is not resolved, proceed to Test Step 3.
3. Check the Supply Voltage to the Sensor A. Turn the keyswitch to the OFF position. B. Disconnect the wiring harness connector for the throttle position sensor. C. Measure the voltage across the following wiring harness connector terminals: - Terminal A (8 V supply) and Terminal B (Digital return)	7.5 VDC	Result: The supply voltage is above 7.5 VDC at the sensor connector. Repair: The wiring is OK. Replace the sensor. Verify that the repair eliminated the problem. Result: The supply voltage is not above 7.5 VDC at the sensor connector. The supply voltage is not reaching the speed control. Repair: Repair or replace the wiring harness. Verify that the repair eliminated the problem.
4. Create a Short at the Throttle Connector A. Turn the keyswitch to the OFF position. B. Install a jumper wire between the appropriate signal and return wire at the sensor connector in order to create a short. - Signal terminal and Return terminal C. Connect Cat ET. D. Use Cat ET to monitor the following codes: - -4 code E. Turn the keyswitch to the OFF position.	Create a Short	Result: A -4 or -6 code becomes active. Repair: The wiring is OK. Replace the failed throttle. Verify that the repair eliminated the problem. Result: A -4 or -6 code does not become active. Proceed to Test Step 5.
5. Create an Open at the Throttle Connector A. Turn the keyswitch to the OFF position. B. Disconnect the appropriate throttle sensor connector. C. Connect Cat ET. D. Use Cat ET to monitor the following codes: - -3 code E. Turn the keyswitch to the OFF position.	Create an Open	Result: A -3 or -5 code becomes active. Repair: The wiring is OK. Replace the failed throttle. Verify that the repair eliminated the problem. Result: A -3 or -5 code does not become active. Proceed to Test Step 6.
6. Check the Supply Voltage to the Sensor A. Turn the keyswitch to the OFF position. B. Disconnect the wiring harness connector for the throttle position sensor. C. Turn the keyswitch to the ON position. D. Measure the voltage across the following wiring harness connector terminals: - Terminal 1 (5 V supply) and Terminal 2 (Analog return) E. Connect the sensor	5 VDC	Result: The supply voltage is approximately 5 ± 0.2 VDC. Proceed to Test Step 7. Result: The supply voltage is not approximately 5 ± 0.2 VDC. Repair: There is a short in the harness to the battery. Repair or replace the wiring harness. Verify that the repair eliminated the problem.
7. Perform the Wiggle Test Carefully following this procedure is the best way to identify the root cause of an intermittent problem. A. Connect Cat ET. B. Use CAT ET to perform the following test: - "Wiggle Test" C. Slowly wiggle the wiring and the connectors between the P2 connector and the sensor. Slowly wiggle the wiring and the connectors between the P1 connector and the sensor. Pay particular attention to the wiring near each connector. Be sure to wiggle all of the wiring. D. As you wiggle the wiring look for the following problems: - Loose connectors or damaged connectors - Moisture on the connectors or the wiring - Damage that is caused by excessive heat - Damage that is caused by chafing - Improper routing of wiring - Damaged insulation	Test	Result: The wiring failed the Wiggle Test. Repair: There is a problem with the wiring harness. Repair or replace the wiring harness. Verify that the repair eliminated the problem. Result: The wiring passed the Wiggle Test. Repair: The problem may be intermittent. Inspect the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for additional information. If the wiring looks OK perform the following procedure: 1. Turn the keyswitch to the OFF position. 2. Disconnect the connectors. Carefully inspect the terminals for proper installation. Make sure that each terminal is clean and dry. 3. Insert a pin into each socket. Verify that each socket grips the pin firmly. Repair any problems. 4. Connect all connectors. 5. Verify that the repair eliminated the problem.

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).