Well, you'll have to use the service manual to trouble shoot your DTC code, but you can check the Up/Down switches, whether the shift motor runs in both directions or not, the gear position switch, the power/ground lines for the display etc, before getting real serious with the multimeter. Those are basics... that must be functional. Also check the vehicle speed sensors, in particular their harness plugs. Leave nothing to chance... put eyeballs on everything.
The FSM shows you how to test the switches and other basics. Warning: turn the ignition OFF before disconnecting/connecting all wiring harness plugs! The CDI/ECM can get spiked if you make a mistake...