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.

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





4. 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 5.
NO - Repair open in the wire between PCM connector terminal A22 and the A9 terminal of the VTM-4 control unit.





5. 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 6.
6. Connect PCM connector A (32P).
7. Connect the battery negative terminal.
8. Turn the ignition switch ON (II).





9. 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.