87 Riviera.....Scanner questions

The scanners (cheapies for AutoZone and O'rielleys) are good for gm cars, OBD 1, WITHOUT AUTOMATIC CLIMATE CONTROL!!@ What scanner do I need to get the codes. I have the little by-pass key but when I put it in and turn the ign. to the on position, all that happens is the check engine light just continues to flash. Help.