Volvo Repair: Check engine light, flash flash flash, example 121

Question
Just bought a 92 940 turbo I changed the air filter but had to un-plug the air mass sensor to get to it. I started the car the check engine light was on took a look and I had forgot to plug the air mass sensor back in I did that but the light still reads check engine any help would be much appreciated.
                   Thanking you in advance
                          Scott

Answer
n the engine bay on the drivers side near the strut tower there is a small black box with a wire attached to it.place the wire in the terminal marked 2.turn ignition key on (not started)press the small button for 1 second and the code will be displayed as a series of flashes.a red led displays the codes.the code will be three digits.small pause in between flashes for a single number long pause between flashes for the next number.example 121 will be flash.....flash..flash.....flash.repeat three times or until first code repeats itself.to erase the code after all codes have been checked hold the button for a good 5 seconds then release the light should light steady,then press for another 5seconds.this will erase the codes.