SCREW 2160029 - Caterpillar

System Operation Description:Use this procedure to troubleshoot any suspect problems with the electrical power supply.This procedure covers the following diagnostic code:
168-02 System Voltage intermittent/erraticA signal from the Engine Control Switch (ECS) is provided to the key switch input P1-70 of the Electronic Control Module (ECM). When the ECM senses battery voltage to the key switch input of the ECM, the ECM will power up. The key switch input receives battery voltage when the ECS is in the AUTO, START or COOLDOWN/STOP positions. If the voltage is removed from the key switch input, the ECM will power down. Cycling power to the key switch input of the ECM will reset the ECM and all active diagnostic codes.The engine ECM requires the keyswitch to be in the AUTO, START or COOLDOWN/STOP position in order to maintain communications with the electronic service tool.Unswitched battery voltage is supplied to the ECM at P1-48, P1-52, and P1-53. The negative battery is supplied to the ECM at P1-61, P1-63, and P1-65.
Illustration 1 g01055154
Typical schematic
Illustration 2 g01058341
P1 ECM connector
(P1-48) +Battery
(P1-52) +Battery
(P1-53) +Battery
(P1-61) −Battery
(P1-63) −Battery
(P1-65) −Battery
(P1-70) Keyswitch Test Step 1. Inspect Electrical Connectors and Wiring
Turn the engine control switch (ECS) to the OFF/RESET position.
Turn the battery disconnect switch to the OFF position.
Thoroughly inspect the J1/P1 ECM connector and the J2/P2 ECM connector. Inspect all of the connectors that are associated with the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors that are associated with the circuit.
Check the ECM connector (allen head screw) for the proper torque of 6.0 N m (55 lb in).
Check the harness and wiring for abrasion and for pinch points from the sensors back to the ECM. Expected Result:All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion and of pinch points.Results:
OK - The connectors and wiring are okay. Proceed to Test Step 2.
Not OK - The connectors and/or wiring are not okay.Repair: Repair the connectors and/or wiring or replace the connectors and/or wiring.Repair CompleteTest Step 2. Check the Voltage to the ECM
Remove ECM connector J1/P1.
Turn the battery disconnect switch to the ON position.
Turn the ECS to the STOP position.
Measure the voltage between P1-48 and P1-61.
Measure the voltage between P1-52 and P1-63.
Measure the voltage between P1-53 and P1-65.
Measure the voltage between P1-70 and P1-65.
Turn the ECS to the OFF/RESET position.
Turn the battery disconnect switch to the OFF position.
Reconnect ECM connector J1/P1. Expected Result:The voltage is 24 3 VDC.Results:
OK - The voltage is 24 3 VDC. The ECM is receiving the correct voltage. Proceed to Test Step 6.
Not OK - The voltage is not 24 3 VDC. The voltage is incorrect. The battery or the alternator may be causing the problem. Proceed to Test Step 3.Test Step 3. Check the Battery Voltage
Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to the Operating Manual, SEHS9249. Refer to Special Instruction, SEHS7633. Expected