my front left abs sensor is going bad in my 99 v70. this seems like something simple to replace.. can i replace this item on my own, or should i let a shop do it?

I have never seen a defective wheel speed sensor in over six years. Maybe a damaged wire, but never a sensor.
On the other hand, a loss of LF wheel speed signal on 99 Volvos is one of the symptoms of a defective ABS unit.

All the ABS control units (Installed on 96 and newer 850, 70 series and S80 models) will eventually fail after they reach 65,000 miles or 5 years. The average is 85,000 miles and/or 6 years for failures.

A dealer will charge from $60.0 to $120.00 to diagnose the problem and about 95% of the cases the mechanic will recommend to replace the ABS control unit.

Check here for more information.
Vitor's Volvo ABS website

Just curious. How did you diagnose it as the front left sensor?

I have read that it is fairly rare for the sensors to go bad and much more common for the ABS controller unit to fail (I have had two controllers fail, one on a 96 850 and one on a 2000 V70).

So I was wondering how you tell if it's a sensor. What are the symptoms?

Thanks, Calvin.

well, my mechanic read it out and said it was a bad ABS sensor, but he is "english as a second language" so maybe he misworded it to me. I'm leaning that it's the ABS Mod., and I was unaware that those things had a limited life...I have one friend with 3 70 series cars and all the ABS mods had to be replaced..

See Vitor's 06/25 reply to your post. If you haven't looked at his site, go to that link and read up on it. He repaired my 850 module 2-3 years ago and it's never given another problem to me or the new owner. My 2000 V70 is currently failing intermitently and I will be sending it to him soon.

My symptoms were:
96 850 Turbo - (about 100K) ABS light came on just after scraping feeling transmitted through the brake pedal, sometimes accompanied by a sound. ABS light would reset - usually at next start up. This happened intermittently until eventually the unit failed completely.
00 V70 - (88K) Same symptoms except it hasn't failed completely yet AND the ABS light is followed by the CEL light and a Vehicle Speed Sensor error.

Sounds like you've already read various posts on the subject, but if not you won't have any difficulty finding LOTS of discussion on this subject!

Regards, Calvin