Code readers..

Which computer code reader will read my 1991 1.0 Firefly?..The GM ones(Equs brand) in Walmart etc. say they won't..(and SO do the people at Equs) YET another place that sells them says that they WILL read those codes..HMmm..I am GUESSING that a Suzuki one..is there a code reader for them?..Thanks..Arnold..