You have a 91?
Do you mean the key does not work in the passenger door? Bad lock.
Do you mean the key in the driver door locks but won't unlock passenger door? Something is wrong.
Listen to see if the power lock in the passenger door makes any attempt to unlock the door. If it tries (noise, some visible lock movement), pull the passenger door panel, you will see the power lock actuator. Probably has rust, spray lube everything you can see...
If it does not try at all to unlock, you might have a bad switch connected to the driver door lock.