How do you fix code 42 on 1994 C2500?

Code 42 on a 1994 Chevrolet C2500 typically indicates a problem with the vehicle's electronic control module (ECM) or the vehicle's security system. To fix this, first check the connections and wiring to the ECM for any signs of damage or corrosion. If the connections are fine, you may need to reset the ECM by disconnecting the battery for a few minutes and then reconnecting it. If the code persists, consider having the ECM tested or replaced, as it may be malfunctioning.