TSR Light and Reading TCM Codes

[Luciendar21]

The short version:
How do I read TCM codes? Can I read them through a standard OBDII reader or do I need to bring the car to a transmission shop?

The long version:

I'm helping my brother figure out the situation with his car (I'm the mechanically inclined member of the family).

His car is a 2001 V70 XC with ~170k mi, purchased last summer (June 2015) with ~160k mi on it.

A few months ago he got the Transmission Service Required message for the first time. He had me look at it and I noticed that his tires were getting pretty bald and the front tires had some uneven wear, so I had him replace all four tires and get an alignment. I also had him bring it to a transmission shop to have the transmission fluid changed.

He had all of this work done at a Midas, along with an oil change. The TSR message cleared and the car has been running smoothly for several months (and about 3k mi). On his drive back to school after Thanksgiving (400mi), the TSR message returned.

I'm trying to figure out my next steps. It seems like I need to get a more clear picture of what is being reported by the TCM, and that means reading (and interpreting) the codes. The car does not appear to have any other symptoms, it shifts through the gears fine (both in drive and manual modes), it isn't sluggish or clunky, and there are no abnormal sounds or smells.

[vtl]

Read the codes, preferably with DiCE+VIDA, but as one hypothetical reason you may have worn transmission selector position sensor. Mine quit one morning at -20F weather when car was only 8 years and 110k miles old. It isn't too bad job to replace, neither the part is too expensive, but in case the budget is tight - you can disassemble the sensor and replace worn parts. The sensor is a pure mechanical switch inside.

[Luciendar21]

Read the codes, preferably with DiCE+VIDA, but as one hypothetical reason you may have worn transmission selector position sensor. Mine quit one morning at -20F weather when car was only 8 years and 110k miles old. It isn't too bad job to replace, neither the part is too expensive, but in case the budget is tight - you can disassemble the sensor and replace worn parts. The sensor is a pure mechanical switch inside.

So, if my quick research on DiCE (Volvo specific reader dongle) and VIDA (Volvo specific software) is correct, I need to buy something like this. Once I have that I can read the codes and determine what is potentially failing.

If it is the sensor, the dash display for the gear will be blank rather than P-R-D-L, etc. If that's the case, I can just replace the sensor (this one at Auto Parts Warehouse), which is relatively easy going through the engine bay, removing the air box and a few other things in the way.