SHAFT 1P6266 - Caterpillar

This procedure covers the following diagnostic codes:
168-00 System Voltage High
168-01 System Voltage Low
168-02 System Voltage intermittent/erraticThis procedure tests whether proper voltage is being supplied to the Electronic Control Module (ECM). 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 three 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 g01302403
Schematic diagram for the electrical power supply
Illustration 2 g01120079
Left side view
(1) P61 customer connector
(2) J1/P1 ECM connectors
Illustration 3 g01302468
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
Illustration 4 g01216338
J61 and P61 terminals that are associated with the electrical power supply
(1) +Battery
(26) Keyswitch
(27) Shutdown
(31) +Battery
(32) +Battery
Table 1
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Check all circuit breakers.
B. Check the battery.
C. Turn the keyswitch to the OFF position.
D. 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.
E. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the electrical power supply.
F. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect", for the correct torque values.
G. 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.
Electrical Connectors and Wiring
Results: The connectors and wiring are OK. Proceed to Test Step 2.
Results: There is a problem with the connectors or wiring.
Repair: 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.
STOP
2. Check the Battery Voltage at the ECM
A. Disconnect the J1/P1 ECM connector.
B. Turn the keyswitch to the ON position.
C. Measure the voltage between P1-52 (Unswitched Positive Battery) and P1-63 (Negative Battery).
D. Measure the voltage between P1-48 (Unswitched Positive Battery) and P1-61 (Negative Battery).
E. Measure the voltage between P1-53 (Unswitched Positive Battery) and P1-65 (Negative Battery).
F. Measure the voltage between P1-55 (Unswitched Positive Battery) and P1-69 (Negative Battery).
G. Measure the voltage between P1-70 (Keyswitch) and P1-63