Illustration 121 Bypass harness

293

TM 9-2320-312-24-2

Troubleshooting Section

g00741090

Illustration 121

Bypass harness

E. Connect ET to the data link connector of the

Note: This bypass harness is only for test

bypass harness and verify that communication

applications. This bypass harness may be left only

is established.

temporarily on the vehicle. The bypass harness can

be used in order to determine if the cause of the

F. Restore all wiring to the original condition after

intermittent problem is interruptions in battery power

testing.

to the ECM or the keyswitch circuit.

Expected Result:

A. Turn the ignition key switch to the OFF position.

Installing the bypass eliminates the problem.

B. Disconnect vehicle harness connector J1/P1

from the ECM.

Note: The status of the ignition key switch will always

indicate "On" while the bypass harness is installed.

C. Connect a bypass harness to ECM connector J1.

Results:

D. Remove the 20 Amp in-line fuse from the

+Battery line of the bypass harness and connect

the unswitched +battery and - battery lines

Yes The symptoms disappear when the bypass

directly to the battery posts.

harness is installed. Also, the symptoms return

when the bypass harness is removed. The

Note: This bypass directly connects the circuit

problem is in the vehicle wiring that supplies

for the ignition key switch to the ECM. The ECM

power to the ECM. Check for aftermarket engine

will remain powered until the connection to the

protection switches that interrupt power. Send the

unswitched battery line "+" is disconnected.

vehicle to the OEM dealer to repair. STOP.

Remove the 20 Amp fuse from the in-line fuse

holder to power down the ECM. Do Not connect the

bypass to the battery posts without first removing

the 20 Amp in-line fuse or do not remove the bypass

Repair: Connect the bypass to another battery

from the battery posts without first removing the 20

and verify if the problem is resolved. If the

Amp in-line fuse.

problem is resolved, the problem is with the

vehicle batteries.