3512B and 3512C Petroleum Generator Set Engines 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

Diagnostic Codes Table
CDL Code and Description	Conditions which Generate this Code	System Response
91-8 Throttle Position Sensor abnormal frequency, pulse width, or period	The Electronic Control Module (ECM) detects an incorrect frequency on the throttle signal or an incorrect duty cycle on the throttle signal. This code is used when the parameter for the "Desired Speed Input Configuration" is configured to "PWM".	The code is logged. The ECM flags the throttle position as invalid data and a default value is used. The engine speed may be limited to high idle.

The speed control provides a throttle signal and a droop signal to the ECM. The output for rated speed is a pulse width modulated signal (PWM) at a constant frequency. The speed signal varies with the position of the speed adjust potentiometer. The output for droop is a PWM signal at a constant frequency. The droop signal varies with the position of the droop adjust potentiometer. The output signal is referred to as a duty cycle or as a PWM signal. The output signal of the speed adjust is expressed as a percentage between 0 and 100 percent. The output signal of the droop adjust is expressed as a percentage between 0 and 10 percent.

The ECM calculates the desired engine rpm from the rated speed signal and the droop signal. The rated speed signal is valid when the duty cycle is in the range of 5 to 95 percent. If the ECM determines that the rated speed signal is invalid, the engine rpm will be set to the programmed low idle.

The droop signal is valid when the duty cycle is in the range of 15 to 85 percent. If the ECM determines that the droop signal is invalid, the engine will run with no droop which is referred to as isochronous mode.

Some applications may choose not to use the speed control. Some applications may use a load sharing module. The load sharing module is configured to provide the engine control with a rated speed signal. The signal has the same characteristics as the above defined signal. Some of these load sharing modules cannot provide a signal until the engine is running. In these cases, troubleshooting should be performed while the engine is running.

Illustration 1	g03320984
Typical schematic

Illustration 2	g03323693
Terminal locations at the P1 ECM connector (P1-5) Digital return (P1-10) Rated speed signal

Illustration 3	g03323694
Terminal locations at the P2 ECM connector (P2-69) Speed droop signal

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 connectors (P1), and (P2). Inspect all of the connectors in the harness from the engine interface connector to the speed control that are associated with the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors, the engine interface connector, and the connector for the EMCP that are associated with the circuit. D. Check the torque of the allen head screws for each of the ECM connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values. E. Check the harness and the wiring for abrasion and for pinch points from the batteries to the ECM.	Connectors	Results: The connectors and wiring appear to be OK. Proceed to Test Step 2 Results: The connectors and/or wiring are not OK. Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Verify that the repair eliminates the problem.
2. Check for Active Diagnostic Codes A. Connect Caterpillar Electronic Technician (ET) to the service tool connector. B. Restore the electrical power to the ECM. C. Monitor the active diagnostic code screen on Cat ET. Check for an active 08 code for the throttle signal. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. D. Turn the main disconnect switch to the OFF position.	Codes	Results: No diagnostic codes are active. Repair: If the above code has been logged, there may be an intermittent problem in the harness or in a connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" in order to troubleshoot intermittent electrical problems. If a problem with the speed control circuit is suspected, proceed to Test Step 3 Results: A 08 diagnostic code is active at this time. The ECM has detected an erratic signal at the input for the throttle signal. Proceed to Test Step 3
3. Check the Supply Voltage to the Speed Control A. Restore the electrical power to the ECM. B. Start the engine. C. Measure the voltage between terminals +Battery and −Battery at the speed control. D. Stop the engine. Turn the main disconnect switch to the OFF position.	24 ± 3.0 VDC	Results: The engine started and the supply voltage is 24 ± 3.0 VDC at the speed control. The speed control is receiving supply voltage. Proceed to Test Step 4 Results: The supply voltage is not 24 ± 3.0 VDC. Repair: The supply voltage is not reaching the speed control. If the engine started, the control relay is receiving electrical power. There is a problem in the harness or the connectors between the output of control relay and the speed control. The problem may be in the ground circuit to the speed control. Perform the following Test Steps: 1. Remove the electrical power from the ECM. 2. Remove the wire from the −Battery terminal at the speed control. 3. Check the resistance between the wire for the −Battery at the speed control and the battery negative post. The correct measurement will indicate that a short circuit condition exists for the circuit. If the resistance measurement indicates a short circuit, the ground circuit for the speed control is OK. There is a problem in the harness or the connectors between the control relay and the speed control. Repair the harness and/or the connectors. Replace parts, if necessary. Verify that the original problem has been resolved. Verify that the repair eliminates the problem. If the measurement did not indicate a short circuit, the problem is in the ground circuit for the speed control. Repair the harness and/or the connectors. Replace parts, if necessary. Verify that the repair eliminates the problem. If the engine does not start, there is a problem in the electrical power supply circuit. Refer to Troubleshooting, "Electrical Power Supply - Test" for details.
4. Check the Throttle Signal at the Speed Control A. Remove the wires from terminal locations 19 (+PWM out) and 20 (−PWM out) at the speed control. B. Restore the electrical power to the ECM. C. Measure the duty cycle of the PWM signal between terminal 19 and terminal 20 at the speed control. Use the speed control potentiometer to vary the speed of the engine during the measurement. The correct duty cycle will remain between 5 percent and 95 percent during the test. The duty cycle will change with the change in the desired engine speed. D. Turn the main disconnect switch to the OFF position. E. Restore the wiring to the original configuration.	5 to 95% duty cycle	Results: The duty cycle measurements agree with the specifications. The speed control is operating correctly. Proceed to Test Step 5 Results: The duty cycle measurements do not agree with the specifications. Repair: The speed control is not operating correctly. Replace the speed control. Verify that the repair eliminates the problem.
5. Check the Throttle Signal at the Engine Interface Connector A. Disconnect the EIC connectors. B. Remove the wires from terminal locations 5 (digital return) and 10 (rated speed) on the speed control side of the engine interface connector. C. Connect the EIC connectors. D. Restore the electrical power to the ECM. E. Measure the percent duty cycle output at the wires from terminal locations 5 and 10 at the engine interface connectors. The correct duty cycle will remain between 5 percent and 95 percent during the test. The duty cycle will change with the change in desired engine speed. F. Turn the main disconnect switch to the OFF position. G. Disconnect the J1/P1 ECM connectors. H. Restore the wiring to the original configuration.	5 to 95% duty cycle	Results: The duty cycle measurements agree with the specifications. The harness and connectors to the EIC are OK. Proceed to Test Step 5 Results: The throttle signal is not reaching the connector. Repair: The signal is OK at the speed control, but not at the EIC. There is a problem in the harness or in a connector. Repair the harness and/or the connectors. Replace parts, if necessary. Verify that the repair eliminates the problem.
5. Check the Throttle Signal at the ECM A. Disconnect the J1/P1 ECM connectors. B. Remove the wire from terminal P1-10 (primary throttle).Restore the electrical power to the ECM. C. Connect the J1/P1 ECM connectors. D. Restore the electrical power to the ECM. E. Measure the duty cycle for the PWM signal at the wire that is for the throttle signal at the J1/P1 ECM connector. Use the speed control potentiometer to vary the speed of the engine during the measurement. The correct duty cycle will remain between 5 percent and 95 percent during the test. The duty cycle will change with the change in desired engine speed. F. Turn the main disconnect switch to the OFF position. G. Disconnect the J1/P1 ECM connectors. H. Restore the wiring to the original configuration.	5 to 95% duty cycle	Results: The duty cycle measurements agree with the specifications. Repair: The harness and connectors that are between the speed control and the ECM are OK. Perform the following Test Steps: 1. Ensure that Cat ET is connected to the service tool connector. 2. Restore the electrical power to the ECM. 3. Monitor the active diagnostic code screen on Cat ET. Check for an active 08 code. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. 4. Turn the main disconnect switch to the OFF position. If the diagnostic code 08 is still active, there is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "Test ECM Mode". Note: Before you consider replacing the ECM, consult with the Dealer Solutions Network (DSN) for assistance. If the diagnostic code 08 is not active, there may be an intermittent problem in the harness or in a connector. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" in order to troubleshoot intermittent electrical problems. Results: The duty cycle measurements do not agree with the specifications. Repair: The signal is OK at the speed control, but not at the input to the ECM. There is a problem in the harness or in a connector. Repair the harness and/or the connectors. Replace parts, if necessary. Verify that the repair eliminates the problem.

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