The 3140 is said to be compatible with OBD-1 from '82 to '95. Perhaps yours is defective. You do have the correct connector to plug into the under-dash diagnostic port...right?scan test..yes..an other issue.. i have a innova 3140g...and pcm doesnt communicate at all....
Code reading should not be confused with a proper scan which would also include access to the data stream.You can scan for codes by jumping two terminals on the diag port with a paper clip by reading blinks on the Check engine light.