This procedure covers the following diagnostic codes:
- 168-00 System Voltage High
- 168-01 System Voltage Low
- 168-02 System Voltage intermittent/erratic
This 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
Illustration 4 g01216338
J61 and P61 terminals that are associated with the electrical power supply