3512B and 3512C Petroleum Generator Set Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engines Electronic Control Module (ECM). Use this procedure if any of the diagnostic codes in Table 1 is active or easily repeated.

Table 1

Diagnostic Codes Table
J1939 Code and Description	Conditions which Generate this Code	System Response
168-3 Battery Potential / Power Input #1 : Voltage Above Normal	Electrical System Voltage : Voltage Above Normal	The code is logged.
168-4 Battery Potential / Power Input #1 : Voltage Below Normal	Electrical System Voltage : Voltage Below Normal	The code is logged.

The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).

Illustration 1	g03320838
Schematic

Illustration 2	g03320926
(P1-52) + Battery (P1-53) + Battery (P1-55) + Battery (P1-63) - Battery (P1-65) - Battery (P1-67) - Battery (P1-69) - Battery

Table 2

1. Inspect the Electrical Connectors and the Wiring A. Turn the main disconnect switch to the OFF position. B. Thoroughly inspect the ECM connectors. Also, thoroughly inspect the other connectors for the electrical power circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the proper procedure for inspecting the connectors and the wiring.	Electrical connectors	Results: The connectors and wiring appear to be OK. Proceed to Test Step 2. Results: There is a problem in the connectors and/or wiring. Repair The connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. Verify that the repair eliminated the problem.
2. Check the Voltage to the ECM A. Disconnect the ECM connector J1/P1. B. Restore the electrical power to the ECM. C. Measure the voltage at the ECM. Measure the voltage between P1-53 and P1-65. Measure the voltage between P1-52 and P1-63.	ECM voltage	Result: The voltage is 24 ± 3 VDC. The ECM is receiving the correct voltage. The problem may be intermittent. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect". Result: The voltage is less than 24 ± 3 VDC. The wiring or components between the battery and the ECM may be preventing the voltage from reaching the ECM. Proceed to Test Step 3
3. Check the Charging Circuit A. Turn the main disconnect switch to the OFF position. A. Check the charging circuit.	Charging circuit	Result: The charging system is OK. Proceed to Test Step 4. Result: The charging system is not OK. There is a problem with the charging system. Make the necessary repairs. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting". Verify that the repair eliminated the problem.
4. Load Test the Battery A. Load-test the battery. Refer to Systems Operation and Testing and Adjusting, "Battery - Test"	Load test	Result: The battery voltage is low or the battery did not pass the load test. Repair: Recharge or replace the faulty batteries. Verify that the repair eliminated the problem. Result: The batteries pass the load test. The measured voltage is between 11.5 VDC and 13.5 VDC for a 12 v system. The measured voltage is between 23.0 VDC and 27.0 VDC for a 24 v system. Proceed to Test Step 5
5. Check the Voltage at the ECM Relay A. Remove the wire from terminal 30 of the ECM relay . B. Restore the electrical power to the ECM. C. Measure the voltage from the wire to the −Battery terminal. D. Turn the main disconnect switch to the OFF position. E. Reconnect the wire to terminal 30 of the ECM relay .	ECM relay voltage	Result: The voltage is 24 ± 3 VDC. Proceed to Test Step 6 Result: The voltage is not 24 ± 3 VDC. Repair: If voltage is present at the breaker for the ECM, repair the wire between the breaker for the ECM and the ECM relay . If voltage is not present at the breaker for the ECM, check the wiring between the battery and the breaker for the ECM. Verify that the breaker for the ECM is not tripped and that the breaker for the ECM is operating correctly. Verify that the repair eliminated the problem.
6. Check the Voltage at Terminal 87A of the ECM Relay A. Remove the wire from terminal 87A of the ECM relay . B. Restore the electrical power to the ECM. C. Measure the voltage from the wire to the −Battery terminal. D. Reconnect the wire to terminal 87Aof the ECM relay .	Voltage	Result: The voltage is 24 ± 3 VDC. Repair: The wiring between the ECM relay and the ECM connector P1 is damaged. Repair the wiring or replace the wiring. Verify that the repair eliminated the problem. Result: The voltage is not 24 ± 3 VDC. Repair: If the coil of the ECM relay is not energized, the contact of the ECM relay is damaged. Replace the ECM relay . 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).