Volvo started using self-diagnostics on its Bosch LH 2.4 engine management systems in 1988 on 700 series non-turbo cars and in Regina-equipped cars. Earlier Bosch LH 2.2 and Turbo cars until 1990 had very limited self-diagnostic capability using an LED tester. In LH 2.4 cars, If a system fault occurs, then the "check engine" lamp will illuminate, signifying the presence of a fault code. For every model year using LH2.4 up to and including the '95s (except 200 series DLs and GLs), you can flash out fault codes, as well as perform input and output testing, through the OBD-I diagnostic connector unit simply by inserting a little self-contained probe and pressing a button. You do not need a special scan tool to read codes. As electronic systems were added to more Volvo models, more socket options and even more diagnostic connectors were added.

Unfortunately, you cannot use a generic code reader on any of these OBD-I cars: you have to manually extract the codes from the systems as noted below. 1996+ cars have the entirely different OBD-II system which requires a computerized code scanner to read codes through a special data link.



The diagnostic connector units for OBD-I systems are small black rectangular boxes mounted in front of the left-side(driver-side in LHD countries) shock tower. Earlier cars have only one unit ("A"); later cars have two ("A" and "B"). Diagnostic connector "A" contains the test terminal probe (the wire mounted on the side of the box in the picture) used in both A and B along with the test button and the LED readout lamp. In diagnostic connector A, socket 1 is for the electronic transmission (if your 960 or 90-series car has the AW30/40), socket 2 for fuel injection or Motronic, socket 3 for ABS, socket 6 for ignition and socket 7 for the instrument cluster. If the 1992+ car is so equipped with connector B, socket 1 is for the climate control, socket 2 for cruise control, socket 5 for the SRS and socket 6 for the memory seats.

For later 1996+ OBD-II equipped cars, the diagnostic connector was changed to an electronic data link and moved from under the hood to in front of the shifter in the console. As a result, you need a computerized scan tool to do everything from checking for codes to resetting the maintenance light. Maintenance light resetting, by the way, was returned to a push-button method in the very late '90s.