OBD 1.5 refers to a partial implementation of OBD-II which General Motors
used on some vehicles in 1994 and 1995 (GM did not use the term OBD 1.5 in the documentation for these vehicles - they simply have an OBD and an OBD-II section in the service manual.)
For example, the 94-95 Corvettes have one post-catalyst oxygen sensor
(although they have two catalytic converters
), and have a subset of the OBD-II codes implemented. For a 1994 Corvette the implemented OBD-II codes are P0116-P0118, P0131-P0135, P0151-P0155, P0158, P0160-P0161, P0171-P0175, P0420, P1114-P1115, P1133, P1153 and P1158.
This hybrid system was present on the GM H-body
cars in 94-95, W-body
cars (Buick Regal, Chevrolet Lumina ('95 only), Chevrolet Monte Carlo ('95 only), Pontiac Grand Prix, Oldsmobile Cutlass Supreme) in 94-95, L-body
(Chevrolet Beretta/Corsica) in 94-95, Y-body
(Chevrolet Corvette) in 94-95, on the F-body
(Chevrolet Camaro and Pontiac Firebird) in 95 and on the J-Body
(Chevrolet Cavalier and Pontiac Sunfire) and N-Body
(Buick Skylark, Oldsmobile Achieva, Pontiac Grand Am) in 95.
Depending on the year and the vehicle, a car with the OBD 1.5 system may have either the older OBD-I connector, or the newer OBD-II connector, but they are electrically identical to each other.
The pinout for the ALDL connection on these cars is as follows:
Female OBD connector pinout
For ALDL connections, pin 9 is the data stream, pins 4 and 5 are ground and pin 16 is battery voltage.
Additional vehicle-specific diagnostic and control circuits are also available on this connector. For instance, on the Corvette 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.
An OBD1.5 has also been used on Mitsubishi cars of '95 '97 vintage.
An OBD1.5 has been used in some 1995 Volkswagen VR6's (Juice Box's GTI)