My SRS light came on yesterday

Manual says drive directly to dealership.

This is a 10 year old car, and this sounds expensive.

Is there something I can check. The Haynes manual mentions

a backup battery and capacitor under drivers seat.

Also the car is normally in garage, but was left out the night

before and temperatures dropped below freezing (into 20's).

Any advice greatly appreciated.

Ours did it at 6-7 years of age. From a dealer, the controller was then (6-ish years ago) $960, plus an hour of labor to install. Wish I'd had the Brickboard then!

Disabling the light is cheap, and then you'd be in the same state as my other (non-SRS)car.

If you demate connectors yourself, be careful. There is a proper procedure, which I don't recall. As you note there is backup power, and the system will deploy despite certain "failures", which might include wire damage in an accident. You don't want to simulate that.

I have had the same problem in the past. I took mine to the dealer, who first tried to read the error codes and reset it ($34.xx). That didn't do the trick, so they pulled the driver's seat and reseated the connectors on the devices under the seat. That did the trick (and cost another $34.xx). Well worth the money in my mind, given that you are playing with an explosive device!

Alternatively, there is also some information about the codes in the 700/900 FAQS.

If in the unlikely even they tell you that you need a new brain box for the SRS system, several people in the Classifieds will be able to provide you with one for less than 1/4 of what the dealer will want.

Good luck!

Good point about explosive device. I'll call Volvo shop (not dealership).