I just replaced four tires on my 97 850 (100K miles). After driving away from the shop I noticed that the ABS light was on steady. I drove back to the shop (large tire store chain) but by the time I made it back, the light had gone out. They inspected the sensors and lines and even put it on a diagnostic computer but couldn't find anything wrong. Of course, as soon as I drove away again the light returned. Since then, the light has been mostly out but ocaisionally, it comes on and stays on for a few miles. Is my ABS computer going bad? I would hate to spend $600 on the computer to find out that it doesn't fix the problem. Is it an easy raplacement? (Something a novice could unplug and plug in with some knowledge of where it's located? Is it easy to access? I have some unrelated work being done by a trusted Volvo tech soon. I'm sure he will give me a much better diagnosis but if the answer is a computer replacement should I pay $150 in labor to have him put one in? Again, if it's easy to get to and it's a simple a matter of unplugging the old and plugging in the new I'm up for the job. If the access or the job is more complicated I'd just assume pay to have it done.