How do you reset cdm on 89 Chevy pickup?

To reset the Computer Diagnostic Module (CDM) on an '89 Chevy pickup, first disconnect the negative battery cable and wait about 15-30 minutes to allow the system to reset. Reconnect the cable, ensuring a tight connection. You may also need to clear any trouble codes using an OBD-I scanner or by removing the fuse for the ECM (Engine Control Module) for a few minutes. Finally, start the vehicle and allow it to idle for a few minutes to let the new settings take effect.