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.