Malcolm,
Your ECM (engine control module) stores codes as faults happen, commonly known as "fault codes". To read the codes you access the ECM memory through a pair of DLCs (data link connectors). They are labelled A & B. They are found attached to the front of the ECM next to the washer reservoir...you are looking for two small boxes that have removable caps on them. The cap on Box "A" has an attached lead to it. This lead is then inserted in any of the ports found on Box A or B. You need a manual to let you know which port is for what, ie: A1 is the transmission, A2 is fuel etc...After inserting the lead, press the button found on Box "A" short but distinctly (about half a second). The led found on the box will give you a three digit code. 1 flash =1, 2 flashes =2, 3 flashes =3 etc...you have to wait while the three digits are played back...have a pencil and paper handy. After noting the code/codes you can then look them up in either a Haynes manual (which does not list them all) or better yet in the Pocket Data Booklet purchased from Volvo ($15). This self diagnostic facility is invaluable and well worth getting familier with. As well as reading codes, you can also input codes...turning off the service light is the most common...however you can go much deeper and reset you odometer or service interval warning...you can even tamper with how your transmission behaves...my advice is to be very carefull when inputting codes...the good news is, your '95 model was the last year that this feature was available. '96 and after owners have to go to the dealer. :( --
Tony G...'94 850GLT, '82 240DL (mint)