What is OBD-1.5

OBD 1.5 is a partial implementation of OBD2 car diagnostic system after manufactures found out OBD1’s drawbacks. It was mostly used on some General Motors in 1994 and 1995. We can still find vehicles with OBD1.5 system today although GM did not use the term OBD 1.5 in the documentation, but simply have an OBD and an OBD-II section in the service manual.
OBD 1.5 has also been used on Mitsubishi 1995 and 1997 vintage, 1995 Volkswagen VR6 and the Ford Scorpio since 1995. To read codes generated by OBD 1.5 system, mechanics will need an OBD 1.5 compatible scan tool.
Besides, additional vehicle-specific diagnostic and control circuits are also available on OBD1.5. For example, Corvettes built between 1994 to 1995 had one post-catalyst oxygen sensor (although they have two catalytic converters), and a subset of the OBD-II codes, but there are interfaces for the Class 2 serial data stream from the PCM, the CCM diagnostic terminal, the radio data stream, the airbag system, the selective ride control system, the low tire pressure warning system, and the passive keyless entry system on them.