G3500H Generator Set Engine Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engines Electronic Control Module (ECM). Also, use this procedure if one of the following diagnostic codes is active or easily repeated.

Table 1

J1939 Code and Description	Comments
158-2 Keyswitch Battery Potential : Erratic, Intermittent, or Incorrect	The engine is running. The battery voltage falls below 18 VDC for one second. The voltage returns above 18 VDC. Three voltage readings in the last 7 seconds were below 18 VDC. The code is logged.
168-3 Battery Potential / Power Input #1 : Voltage Above Normal	The battery supply voltage is greater than 32 VDC on 24 VDC systems for 0.5 seconds. The ECM has been powered for 3 seconds. The engine is running for at least 3 seconds. The code is logged.
168-4 Battery Potential / Power Input #1 : Voltage Below Normal	The 24 VDC voltage falls below 18 VDC for 0.5 seconds. The 24 VDC voltage must return above 18.2 VDC for 3 seconds in order for the diagnostic to reset. The engine is running for at least 3 seconds. The code is logged.

Illustration 1	g03746407
For the complete circuit details, refer to the full schematic.

Table 2

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 -2, -3, or -4 code is active or logged. Proceed to Test Step 2.
2. 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 3. 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 3.
3. Check the Voltage to the ECM A. Turn the main disconnect switch to the ON position. B. Measure the voltage at the ECM between the following terminals: - A-C1 terminal 48 and Engine ground - A-C1 terminal 52 and Engine ground - A-C1 terminal 53 and Engine ground -A-C1 terminal 55 and Engine ground -A-C1 terminal 70 and Engine ground	Voltage	Result: Battery voltage measured less than 18 VDC but was greater than 0 VDC on one or more of the ECM inputs. Proceed to Test Step 4. Result:0 VDC was measured on one or more of the ECM inputs for battery voltage. Repair: There is a problem with a fuse, connectors, or wiring in between the batteries and the ECM. Repair or replace the wiring harness and/or fuse.
4. Check the Charging Circuit A. Turn the main disconnect switch to the ON position. B. Start the engine. C. Check alternator or battery charging system output voltage.	Charging Circuit	Result: The charging system output voltage is OK. Proceed to Test Step 5. Result: The alternator or battery charging system output voltage is less than 24 VDC. Repair: Repair or replace the damaged alternator or charging circuit components. Refer to Troubleshooting, "Alternator Problem (Charging Problem and/or Noisy Operation)" for additional information. Result: The alternator or battery charging system output voltage is greater than 32 VDC. Repair: Repair or replace the damaged alternator or charging circuit components. Refer to Testing and Adjusting, "Electrical System" for additional information. If the problem is not resolved, proceed to Test Step 5.
5. Inspect the Batteries A. Charge the batteries, if necessary. Refer to Special Instruction, SEHS7633, "Battery Test Procedure" for additional information. B. Load-test the batteries. Refer to Special Instruction, SEHS9249, "Use of 4C-4911 Battery Load Tester for 6, 8 V and 12 V Lead Acid Batteries" for additional information.	Batteries	Result: The batteries are NOT OK. Repair: Repair or replace the batteries.

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).