People wanting to reset lights beware!!! [850][92-95] ... posted by Sin  on Wednesday, 28 February 2001, at 4:12 a.m.
 

                       DO NOT CONFUSE "SERVICE LIGHT" WITH "DIAGNOSTIC LIGHTS" i.e. "CHECK
                       ENGINE," "LAMBDA," etc. WHEN RESETTING LIGHTS!!!

                       Suffering from insomnia once again, I went to the "good book," or better known as the Haynes manual
                       for the 850.

                       Started reading and realized something. As many of you already know, depending on which engine you
                       have, there are two different ways to read and three different ways to reset the lights. It all depends on
                       which system you are running and which kind of light you are resetting.

                       Depending on model, 850's are either fitted with the Motronic 4.3 system, the Motronic 4.4 system or
                       the Fenix 5.2 system. The Motronic 4.3 was fitted on 20 valve engines and some versions of the B5254
                       S engine, from 92-95. The Motronic 4.4 was fitted on the 96-97 850s in the majority of the B5254 S
                       engines. The Fenix 5.2 was fitted on the 10 valve non-turbo engines.

                       For all 850s, one way to read fault codes (that set off diagnostic lights) can be with a scanner tool.
                       Those with the earlier models 92-96 (some 96's, not all) that have either the Motronic 4.3 or the Fenix
                       5.2, will have the diagnostic tool in the engine compartment. A small number will not. All of the 850s
                       with the Motronic 4.4 or models from 95-97 (notice the overlap in years) do not have the diagnostic
                       tool in the engine compartment and require the scanner tool to reset fault codes.

                       Now to get back to the difference between a "service light" and one many of the "warning lights." The
                       Service Light is the little light that says "Ser-vice" on it. This light comes on automatically when either
                       12,500 miles, 1000 engine hours, or 18 months approaches (actually a complicated calculation of the
                       three). Now this light can be reset using one of the two following methods; depending on which model
                       you have.

                       If you are lucky enough to have one of the earlier 850's with an actual reset button hidden behind a small
                       rubber grommet, then this is simple. Simply pry of the grommet trying not to damage anything in the
                       process, and depress the button behind it. If not, do the 4 - 1 - 5 - 1 ----- method very well explained
                       on Volvospeed/Bay 13.

                       Now for the other kind of light. These diagnostic warning lights only occur when a fault has been
                       detected by the ECU. These faults can range from an intake problem, to a faulty part, to missing signals
                       and more. And here's where the explanation of which fuel system comes into play.

                       The Motronic 4.3 system and the Fenix 5.2 can be reset using the diagnostic tool (as long as they come
                       with the diagnostic tool). However, each fuel system has its own method for resetting the fault codes and
                       the Motronic 4.4 cannot be reset by the diagnostic tool as it does not come with one. In order to reset
                       the warning light on the Motronic 4.4, a scanner tool must be used.

                       For the Motronic 4.3 and Fenix, one must first read the codes and then reset them. Great instructions
                       are found in both the Haynes manual and the Volvospeed/Bay 13 site.

                       I appologize for sounding stupid to many of the newer-FWD veterans. I just wanted to make sure
                       people that didn't know the difference realised that there are two different ways of resetting the various
                       warning/service lights on the 850.