P1656

DTC P1656: Problem in PCM-to-VTM-4 Control Unit Communications Circuit

NOTE:
^ Record all freeze data and review General Troubleshooting Information before you troubleshoot.
^ This code is caused by an electrical circuit problem and cannot be caused by a mechanical problem in the transmission.

1. Turn the ignition switch OFF.
2. Disconnect PCM connector A (32P) and the A (22P) connector from the VTM-4 control unit.





3. Check for continuity between PCM connector terminal A22 and the A9 terminal of the VTM-4 control unit.
Is there continuity?
YES-Go to step 4.
NO-Repair open in the wire between PCM connector terminal A22 and the A9 terminal of the VTM-4 control unit.





4. Check for continuity between the A9 terminal of the VTM-4 control unit and body ground.
Is there continuity?
YES-Repair short to ground in the wire between PCM connector terminal A22 and the A9 terminal of the VTM-4 control unit.
NO-Go to step 5.
5. Connect PCM connector A (32P).
6. Turn the ignition switch ON (II).





7. Check for voltage between PCM connector terminal A22 and body ground.
Is there about 10 V?
YES-Check for loose terminal fit in the PCM connectors and the VTM-4 control unit connectors. If necessary, substitute a known-good PCM and recheck.
NO-Replace the PCM.