PISTON 0997150 - Caterpillar

Use this test to troubleshoot any suspect problems with power to the Electronic Control Module (ECM).This procedure covers the following diagnostic codes:
168-00 "System Voltage High"
168-01 "System Voltage Low"
168-02 "System Voltage intermittent/erratic"Use this test if there are intermittent engine shutdowns or if a difficulty in starting is not accompanied by loss of electrical accessories. Engine shutdowns that are accompanied by a loss of other electrical accessories indicate a problem in the keyswitch. This does not indicate a problem in the wiring at the engine's ECM. Verify that there are no problems with the starting system or the charging system before you use this test.The ECM receives battery voltage through the main relay and the 15 Amp fuse for the engine control. Switched 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.The ECM receives the input from the keyswitch at P1-70 when the keyswitch is in the ON position or in the START position. When the ECM detects battery voltage on P1-70, the ECM will electrical powerup. When battery voltage is removed from P1-70, the ECM will electrical powerdown.The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with the Caterpillar Electronic Technician (ET).
Illustration 1 g01198705
Typical schematic
Illustration 2 g01112632
P1 ECM connections
(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
Remove the electrical power from the ECM.
Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Refer to the