C8.7 and C12.9 Marine Engines Caterpillar

Use this procedure to troubleshoot a problem 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
158-3 Keyswitch Battery Potential : Voltage Above Normal	The keyswitch voltage is above the trip point
158-4 Keyswitch Battery Potential : Voltage Below Normal	The keyswitch voltage is below the trip point
168-0 Electrical System Voltage : High	The battery supply voltage is above the trip point.
168-1 Electrical System Voltage : Low	The battery supply voltage is below the trip point.

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Remove electrical power from the engine ECM. B. Thoroughly inspect connectors (1) and (2). Inspect all the connectors that are 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 for each of the ECM connectors 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 and/or wiring	Result: The harness and wiring appear to be OK. Proceed to Test Step 2. Result: The connectors and/or wiring are NOT OK. Repair : Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all the seals are properly in place and ensure that the connectors are coupled completely. Verify that the repair eliminates the problem. If the problem is not resolved, proceed to Test Step 2.
2. Check the Battery Voltage at the ECM A. Remove electrical power from the ECM. B. Disconnect the J1/P1 ECM connector. C. Restore electrical power to the ECM. D. Turn the keyswitch to the ON position. E. Wiggle the wires in the harness while performing the following test steps. a. Measure the voltage between P1-25 (+Battery) and P1-3 (−Battery). b. Measure the voltage between P1-49 (+Battery) and P1-28 (−Battery). c. Measure the voltage between P1-73 (unswitched +Battery) and P1-75 (−Battery). d. Measure the voltage between P1-69 (keyswitch) and P1-75 (−Battery).	Voltage between 12 VDC and 27 VDC.	Result: The ECM is OK. Repair : There may be an intermittent electrical problem in a harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect". Result : Battery voltage out of range - The voltage is not correct for one of the battery circuits at the ECM. Proceed to Test Step 3. Result : Keyswitch voltage out of range - The voltage is not correct for the keyswitch circuit at the ECM. Proceed to Test Step 4.
3. Check the Batteries A. Measure the no-load battery voltage at the battery posts. B. Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to Special Instruction, SEHS9249, "Use of 4C-4911 Battery Load Tester for 6, 8 Volt and 12 Volt Lead Acid Batteries" and Special Instruction, SEHS7633, "Battery Test Procedure".	Batteries	Result: The batteries pass the load test. Repair : The batteries are OK. There is an open circuit or excessive resistance in the wiring or connections between the batteries and the ECM. Verify that the 15 Amp circuit breaker for the ECM is not tripped. Verify that the connections at the bus bars that are for the battery are clean and tight. Repair the connectors or wiring and/or replace the connectors or wiring between the battery and the J1/P1 ECM connector. 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 eliminates the problem. If the problem is not resolved, proceed to Test Step 4.
4. Check the Voltage from the Keyswitch to the ECM A. Remove electrical power from the ECM. B. Remove the wire from the terminal R of the keyswitch. C. Restore electrical power to the ECM. D. Turn the keyswitch to the ON position. E. Measure the voltage on terminal B of the keyswitch to the negative battery contact. F. Measure the voltage on terminal R of the keyswitch to the negative battery contact. G. Remove electrical power from the ECM. H. Turn the keyswitch to the OFF position.	Voltage	Result: The voltage is OK. Repair : There is a problem in the circuit that is between the keyswitch and the ECM. Repair the wiring and/or the connectors. Verify that the repair eliminates the problem. Result: The voltage on terminal B is NOT OK. Repair : If voltage is not present on terminal B, repair the circuit that is between the +Battery and the keyswitch. Check the circuit protection for the circuit. Verify that the problem is eliminated. Result: The voltage on terminal R is NOT OK. Repair : If voltage is present on terminal B of the keyswitch but not present on terminal R, replace the keyswitch. Return all wiring to the original configuration. Verify that the problem is eliminated.

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).