ENGINE AR-PRIMARY 3924129 - Caterpillar

Batteries give off flammable fumes which can explode.To avoid injury or death, do not strike a match, cause a spark, or smoke in the vicinity of a battery.
Do not connect the bypass harness to the battery until all of the in-line fuses have been removed from the Battery+ line. If the fuses are not removed before connection to the battery, a spark may result.
Note: This bypass harness is only for test applications. This bypass harness must be removed before the application is released to the customer. The bypass harness can be used in order to determine if the cause of the intermittent problem is interruptions in battery power to the ECM or to the keyswitch circuit.
Illustration 3 g01803954
Schematic for the bypass application harness
Turn the keyswitch to the OFF position.
Disconnect the P1 connector from the ECM.
Connect a bypass harness to the ECM.
Remove the fuses from the Battery+ wire of the bypass harness and connect the Battery+ and the Battery- wires directly to the battery terminals.Note: This bypass directly connects the circuit for the keyswitch to the ECM. The ECM will remain powered until the connection to the unswitched battery+ line is disconnected. Remove the fuses from the in-line fuse holder to power down the ECM. Do not connect the bypass to the battery terminals or do not remove the bypass from the battery terminals without first removing the in-line fuses.
Use a multimeter to measure the voltage between P2:46 and ground. The voltage should be +5 Volts DC.Note: Remove the bypass harness and restore all wiring to the original condition after testing.Expected Result:If the measured voltage between P2:46 and ground is +5 Volts DC, installing the bypass has eliminated the fault.Results:
OK - The symptoms disappear when the bypass harness is installed. Also, the symptoms return when the bypass harness is removed. The fault is in the wiring for the application that supplies power to the ECM. Check for aftermarket engine protection switches that interrupt power. Send the machine to the OEM dealer to repair.STOP
Not OK - Repair: Perform the following procedure:
Connect the bypass to another battery and verify if the fault is resolved. If the fault is resolved, the fault is with the batteries on the application.
If the fault still exists, make sure that the latest flash file for the application is installed in the ECM. Refer to Troubleshooting, "Flash Programming".
Contact the Technical Communicator.Note: This consultation can greatly reduce the repair time.
If the Technical Communicator recommends the use of a test ECM, install a test ECM. Refer to Troubleshooting, "Replacing the ECM".
Use the electronic service tool to recheck the system for active diagnostic codes.
If the fault is resolved with the test ECM, reconnect the suspect ECM.
If the fault returns with the suspect ECM, replace the ECM.
Use the electronic service tool in order to clear all logged diagnostic codes and then verify that the repair eliminates the fault.STOP