3512B and 3512C Petroleum Generator Set Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle signal from the PWM signal convertor. Also, use this procedure if the diagnostic code 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 abnormal throttle signal for 5 seconds.	The code is logged.

The direct fuel control mode enables the engine to be controlled by an external governor. Install the components of the signal converter for the direct fuel control in order to operate in direct fuel control mode. The "Direct Fuel Control Mode" parameter must be programmed to "Enabled" in order for the ECM to respond properly to the external governor.

The input to the signal converter is a 0 to 200 mA signal. The signal is received from the external governor. The output signal from the signal converter is a Pulse Width Modulated signal (PWM).

The output signal varies with the current to the signal converter. The ECM calculates the desired fuel from the PWM signal.

The duty cycle for a valid signal is between 5 and 95 percent. If an invalid signal is received, the engine will automatically be set to a minimum fuel setting and the engine will shut down.

The following functions are not used in direct fuel control mode.

• Low idle

• Crank terminate speed

• Cooldown speed

Illustration 1	g03323133
Schematic for the direct fuel control mode (typical example)

Illustration 2	g03323144
Terminal locations at the J1/P1 ECM connector (P1-5) Digital return (P1-10) Throttle signal

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect Electrical Connectors and Wiring A. Turn the main disconnect switch to the OFF position. B. Thoroughly inspect the ECM connectors J1/P1. Inspect all of the other connectors in 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 connector that are associated with the circuit. D. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values. E. Check the harness and the wiring for abrasion and for pinch points.	Connectors	Results: The connectors and wiring are OK. Proceed to Test Step 2 Results: The connectors and/or wiring are not OK. Repair: The connectors or wiring and/or replace the connectors or wiring. Verify that the repair eliminates the problem.
2. Check the Current Input to the Signal Converter A. Restore the electrical power to the ECM. B. Measure the current to the signal converter. Note: Some external governors may only be able to output approximately 150 mA. Do not recognize this output as a problem with the external governor.	0 to 200 mA	Results: The current is within 0 to 200 mA. Proceed to Test Step 3 Results: The current is not within the correct range. Repair: Replace the external governor that is supplying the controlling current. Verify that the repair eliminates the problem.
3. Check the Voltage at the Battery A. Turn the main disconnect switch to the OFF position. B. Measure no-load battery voltage at the battery terminals. Refer to Systems Operation/Testing and Adjusting, "Test Tools for the Electrical System" for the proper procedures to check the batteries. C. Test the batteries. Use the 4C-4911 Battery Load Tester. Refer to the Operating Manual, SEHS9249Refer to Special Instruction, SEHS7633	24 ± 3 VDC	Results: The voltage measures 24 ± 3 VDC. Proceed to Test Step 4 Results: The voltage is not 24 ± 3 VDC. Repair: The batteries or the alternator are causing the problem. Recharge the batteries or replace the batteries. Refer to Systems Operation/Testing and Adjusting, "Electrical System" Verify that the repair eliminates the problem.
4. Check the Voltage at the Signal Converter A. Restore the electrical power to the ECM. B. Connect one probe of the voltmeter to the +Battery terminal at the signal converter. C. Connect one probe of the voltmeter to the terminal for the sensor return at the signal converter.	24 ± 3 VDC.	Results: The voltage is 24 ± 3 VDC. Proceed to Test Step 5 Results: The voltage is not 24 ± 3 VDC. Repair: Check the wiring and/or the connectors that are between the battery and the signal converter. Repair the wiring and/or connectors. Verify that the repair eliminates the problem.
5. Check the Throttle Position A. Connect Caterpillar Electronic Technician (ET) to the service tool connector. B. Turn the ECS to the STOP position. C. Observe the throttle position reading on Cat ET. D. Vary the current to the signal converter.	Throttle	Results: The throttle position on Cat ET corresponds with the current input. Repair: The throttle position on Cat ET corresponds with the current input. Results: .The throttle position does not correspond to the current input. Proceed to Test Step 6
6. Check the Signal from the Signal Converter A. Turn the main disconnect switch to the OFF position. B. Remove the signal wire from the signal converter. C. Turn the main disconnect switch to the ON position. D. Set the multimeter to "VDC" E. Press the "Hz" button twice so that the "%" symbol is displayed. F. Place one probe on the signal wire of the signal converter. G. Place the other probe on the −Battery terminal of the signal converter. H. Monitor the output of the percent duty cycle from the signal converter. I. Adjust the current input from a low current setting to a high current setting. Note: The throttle position on Cat ET will not match the percent duty cycle on the multimeter.	Signal Converter	Results: The correct signal is being supplied. Proceed to Test Step 7 Results: The duty cycle is not correct on the multimeter. Repair: Temporarily install another signal converter. Verify that the problem is no longer present. Reinstall the old signal converter. If the problem returns, replace the signal converter. Verify that the repair eliminates the problem.
7. Check the Signal at the ECM A. Turn the main disconnect switch to the OFF position. B. Replace the signal wire on the signal converter. C. Remove the signal wire from terminal P1-66 at the ECM connector. D. Reconnect ECM connector J1/P1 E. Turn the main disconnect switch to the ON position. F. Set the multimeter to "VDC" G. Press the "Hz" button twice so that the "%" symbol is displayed. H. Monitor the output of the percent duty cycle from the signal converter. Connect the meter between the signal wire at ECM connector P1-66 and a good source of engine ground. I. Vary the input current to the signal converter.	Duty Cycle	Results: The duty cycle is correct. Repair: There appears to be 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. Results: The duty cycle is not correct. Repair: There is a problem in the wiring between the signal wire at ECM connector P1-66 and the signal converter. Repair the wiring or replace the wiring. Verify that the repair eliminates the problem.