Recently picked up a 1999 V70 XC. All was good for about 300 miles. Pulled out of a driveway and the flashing trans arrow and check engine light went on. Had my regular car shop check it out and they referred me to a transmission shop. To make a long story short,the trans shop has checked out the wiring from trans to TCM and all seems OK. Before switching out the TCM and reinstalling the harness verification of solenoid resistance is needed. So far he is coming up with:
SL at 11.8/11.9, S1 at 13.4 , S2 at 13.7 , and STHG at 3.4 . He does not know what the STHG designation is. The transmission is a AW 50 42 LE . Any input on the solenoid resistance specs and what the STHG is would be greatly appreciated.

Your mechanic should have given you some 'codes' before he sent you on your way. The STH = Short To Voltage In Line Pressure Solenoid (STH) Circuit
124 Short To Ground In Mode Selector Switch Circuit
131 Open Or Short To Ground In Line Pressure Solenoid (STH) Circuit

An electrical fault? Any good tranny shop should know how to repair this and not charge you an arm or leg.

Klaus,
Thanks for the comeback. There were some codes but I left them in the car that is still at shop. The trans guy is a straight shooter, just does not have a lot of hands on experience with volvo and limited access to tech info. What would you recommend as the next course of action ?

Verify that the fluid level is good. And, good color. Have you tried 'rowing' the shifter from R to L about 20 times with the engine off? The rowing cleans off the contacts at the PNP.

If the mechanic is not familiar with AW50s, he is either a really good guy or wants to learn in a hurry.

Klaus,
If the PNP is faulty would this also cause the trans to go into the "limp" mode ?

A faulty PNP immediately causes limp home mode. Rowing the shift lever usually clears it for a little while. Rowing doesn't hurt anything so long as the engine is off while doing it, so give it a try. If the arrow doesn't clear by rowing, then you have a solenoid problem which may or may not be costly to repair - haven't done that yet.

Just got the codes, all are preceded by PO..753, 758, 748, and Pl 618. All resistance specs from solenoids are in range and all wiring from trans to TCM check out OK.

I agree with Bud, there is an electrical problem. It could be a bad ground wire connection...

Unfortunately, those codes are solenoid-related codes. None of them is for the PNP switch. It is very possible that there is a wiring/connector problem that is causing the codes to appear all at once like this especially if the resistances of the solenoids all measure with in spec. It would be useful to find a shop that has a VIDA/DiCE setup. It would be more useful in interpreting the codes.
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1966 122s, 1968 142s, 1969 144s, 1979 245dl, 1989 244gl

Seems to be narrowed down to the Pressure Control Solenoid. I am on the East Coast in New Jersey. Any thoughts on where I get best purchase this part ?

Fluid level is good, however it is dirty. To show my ignorance what is the PNP ?