BODY 9S4148 - Caterpillar

Table 1
Diagnostic Trouble Codes
J1939 Code CDL Code Code Description Comments
168-2 168-2 Battery Potential / Power Input #1 : Erratic, Intermittent, or Incorrect This code indicates that the battery circuit to the ECM is intermittent.
168-3 168-3 Battery Potential / Power Input #1 : Voltage Above Normal The ECM detects voltage that is above the acceptable value.
168-4 168-4 Battery Potential / Power Input 1 : Voltage Below Normal The ECM detects voltage that is below the acceptable value.
Follow the troubleshooting procedure to identify the root cause of the fault. The ECM receives electrical power (battery voltage) through the wiring that is supplied by the manufacturer of the application. Unswitched battery+ voltage is supplied through P1: 48, 52, 53, 55, and 57. The battery- is supplied through P1: 61, 63, 65, 67, and 69. 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 at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down.An intermittent power supply to the ECM can occur on either the positive side or on the negative side of the battery circuit. The connections for the unswitched battery+ may be routed through a dedicated protection device (circuit breaker).Some applications may be equipped with an engine protection shutdown system or an idle timer shutdown system that interrupts electrical power to the keyswitch. The engine protection shutdown system can be an aftermarket device and the idle timer shutdown system can be external to the ECM. Some of these systems will not supply power to the ECM until one of the following conditions is met:
The engine is cranking.
The engine oil pressure achieves acceptable limits.
An override button is pressed.These devices may be the cause of intermittent power to the ECM. These devices may also stop the engine.Usually, battery power to the diagnostic connector is available and the battery power to the data link connector is independent of the keyswitch. Therefore, although the electronic service tool can be powered up, there may be no communication with the engine ECM. The engine ECM requires the keyswitch to be in the ON position to maintain communications. The ECM may power down a short time after connecting the electronic service tool if the keyswitch is in the OFF position.For intermittent faults , temporarily bypassing the application wiring may be an effective means of determining the root cause. If the symptoms disappear with the bypass wiring, the application wiring is the cause of the fault. A means of bypassing the application wiring is explained in this test procedure. This procedure is especially important for applications that do not provide dedicated circuits for the unswitched battery and the connections for the keyswitch.
Illustration 1 g06151636
Typical example of the schematic for the electrical power supply circuit
Illustration 2 g01981196
View of the pin locations on the P1 connector for the ignition keyswitch and battery supply circuit
(48) Battery+
(52) Battery+
(53) Battery+
(55) Battery+
(57) Battery+
(61) Battery ground
(63)