GUARD AS 8P6274 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engine's Electronic Control Module (ECM) or if any one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table    
Code    Conditions which Generate this Code    System Response    
168-0 Electrical System Voltage : High     The battery supply voltage is greater than 32 VDC for 0.5 seconds.
The engine's ECM has been powered for three seconds.
The engine is not being cranked.     The code is logged.    
168-1 Electrical System Voltage : Low     The battery supply voltage is less than 18 VDC for 0.5 seconds.
The engine's ECM has been powered for three seconds.
The engine is not being cranked.    
168-2 Electrical System Voltage : Erratic, Intermittent, or Incorrect     The engine is running. The battery voltage falls below 6 VDC and the voltage returns above 9 VDC for three voltage readings in the last seven seconds.    Unswitched battery voltage is supplied through the customer connector to the ECM at P1-48, P1-52, P1-53, and P1-55. The negative battery is supplied to the ECM at P1-61, P1-63, P1-65, and P1-69. The ECM receives the input from the keyswitch at P1-70 when the keyswitch is in the ON position or the START position. When the ECM detects battery voltage at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down.The cause of an intermittent power supply to the ECM can occur on either the positive side or the negative side of the battery circuit. Both sides are routed from the ECM to the battery. The four connections for the unswitched +Battery should be routed through a dedicated protective device (circuit breaker).The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with the electronic service tool.
Illustration 1 g01820735
Schematic diagram for the electrical power supplyTest Step 1. Inspect the Electrical Connectors and the Wiring
Check all circuit breakers.
Check the battery.
Remove electrical power from the engine ECM.
Turn the keyswitch to the OFF position.
Illustration 2 g01167488
ECM connectors (typical example) (1) J1/P1 ECM connectors
Thoroughly inspect connectors (1) and (2). Inspect the connections for the battery and the connections to the keyswitch. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 3 g01745555
P1 terminals that are associated with the electrical power supply (P1-44) Shutdown (P1-48) +Battery (P1-52) +Battery (P1-53) +Battery (P1-55) +Battery (P1-61) −Battery (P1-63) −Battery (P1-65) −Battery (P1-69) −Battery (P1-70) Keyswitch
Perform a 45 N (10 lb) pull test on each of the wires that are associated with the electrical power supply.
Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
Check the harness and wiring for abrasions and for pinch points from the battery to the ECM. Also, check the harness and wiring for abrasions and for pinch points from the keyswitch to the ECM.Expected Result:All connectors, pins, and sockets