Ok folks I have tried just about everything to get a 4th gear in my Volvo.

The relay clicks, I have 12 volts at the solenoid. This afternoon I tried one more strange thing. I un-bolted the solenoid from the transmission and got a can of compressed air and did the following.

With the ignition key turn on (Engine off) I grounded the solenoid under the car and heard a click. Then I took the compressed air can and sprayed air into one of the holes in the solenoid. Out of the other hole air came out. That means the solenoid is working. Then I pressed the up arrow switch on the gear shifter and tried to spray air into the same hole. No air came out of the other hole. So I confirmed that the solenoid was working properly when the button is pressed to lockout the 4th gear.

Could my transmission just be BAD and not allow the 4th gear to work?

The oil is new and at the proper level and the transmission shifts gears fine. The car has 228K miles and runs great. I bought the car last April with the NO 4th gear working. The previous owner did not notice that it did not shift into 4th gear.

Any suggestions would be appreciated.

Should I buy a new relay?