The story of my 850 & the ATF change that worked...

Here's my story, which may or may not help.

I bought my 850 with a mileage of 55000 kilometres.

Soon after purchasing it I noticed I had some slipping when engaging into D from any of N/R/P, and only when warm.

I pulled three codes (* how to do this?) out of the diagnostic system -

(* At this link, Volvospeed lists the US Part number for the Pocket data booklet. In Australia the booklet for the 1991-1998 850s is part no. TP 0302037)

3-1-3 PNP  gear position sensor fault
2-2-3 throttle position sensor fault
1-3-4 ignition module load signal faulty

When you get all of the codes (note!) out of the diagnostic system, you should then reset the system so that you can see if the faults return. This is the standard way of responding to diagnostic codes. In my case, no codes returned to me after resetting. Even after weeks went by this was still the case, even though the fault was still occurring intermittently. So these codes weren't telling me much, except that either

1. At one point in time the fault (whatever it was) was bad enough to set off the diagnostic sensors, or
2. The codes were just due to a "random abberation" such as a voltage spike.

In my case it is difficult to determine which was the case. The fact that the codes didn't come back points to (2) but the fact that the codes were in line with symptoms displayed by the car points to (1).

The colour of my ATF (Auto transmission fluid) was a brown colour, and smelt a little off but more like fresh fluid that burnt fluid. It was likely that the previous owner had never changed it.

1.

I went to a transmission specialist who said that the transmission was stuffed.
There was nothing to do but overhaul or replace it.
It would just get worse and worse until I was forced to fix it (if I wanted it to move, that is...)
He said that changing the fluid would not help, and would be likely to make it worse.
They did a lot of 850s, but even more BMW's.
He believed that if there were more frequent intervals specified for changing of the ATF, these problems would be far less likely to occur at all.
2.
I went to an independent Volvo specialist who said that they had never had an 850 into the workshop with transmission problems, but had replaced lots of PNP's (- gear position selector switches). They didn't think changing fluid would do anything to help with problems I described (it wouldn't replicate when they drove it).


3.

I went to another transmission specialist who once again said much in common with (1) above: once again the transmission was stuffed. They diagnosed a different internal problem to the first tranny shop but also said that changing fluid wouldn't help but rather would make it worse. They also said additives were & absolute no-no & would perhaps completely stuff the tranny in a week.


4.

I asked the "Gods of Brickboard" & received quite a number of different responses.
You can see them here.
 
 

The solution 

I was lucky and had the best case scenario. I fixed the transmission with a simple change of transmission fluid.