Ok. I am out of my mind.
My 98 S90 has been great! Now I have a weird situation.
The transmission lights blinking came on. It still drove fine, but the up arrow was on and the blinking W-S-E lights on the shifter were on.
i take it to the volvo repair guy and they say. There is nothing wrong, the sensor may have been whack, so they cleaned it. (?)
Its ok for a while, then it happens again. This time they remove the dash bulb as they say there is nothing wrong again.
NOW...the W-S-E blinks. The tranny occasionally does not go into gear from at a light or standing stop. And the W-S-E lights blink and it will not go into "W" mode.
Help??????

 

PNP switch. That's all you need to know. Very common problem. Search here.

 

I took this into a Volvo Tech and He disconnected the light. (Go Figure) Said...Nope the PNP switch is fine. Awesome!

 

Did you take off the bumper or just drill through the whole bumper--there is a spot where it feels it is about 2" thick....Any advice/experience would be appreciated.

 

OK....so I take it back and the WSE lights are blinking, but the tranny is functioning. (It missed 1st a time or two so I was worried). THe tech says all is well, no PNP switch needed, I Dunno....was the diagnosis. I asked him while he is there to service the tranny, cleaning, change screen and fluids. He says ok, on this one it should be ok. It has 283,000 miles.
After service..lights no longer blinking...tranny is perfect......go figure.

 

There is more than one "fault" mode for the tranny.

I think maybe you may not have been experiencing the PNP problem, which sends the tranny into the worst, most harsh fault mode: there is no pressure regulation (hard shifts) and there is no shifting in forward gears (you manually select 3 or 4.)

If this were my car I would be asking the tech what fault codes the tranny reported. If he is not reading these out, I think he is guessing.