My 2000 C70 ABS warning light came on. I pulled all of the sensors at the wheels and made sure that they were clean; blew off the tone rings with compressed air and checked by eye that they were free of dirt, mud, grease, and anything else that might interfere. Having read on this forum and the Matthews forum that folks believe the ABS module was often the problem with solder joints failing over time, I went ahead and ordered a replacement module from Midwest ABS. It came (along with a torx socket to be returned with the core...I didn't need it because I had a set, but it was a thoughtful loaned tool) and I installed it whilst returning my core module (with torx) to Matt. The light warning light stayed on. Since I believed the references for Matt's work on these forums, I went looking for a sensor problem. I found it on the right front sensor connector behind the coolant overflow tank. One of the 2 wires was broken off. I immediately ordered the correct part from Rock Auto. The next day Matt emailed me to tell me that he had read my old ABS module and found the error message for the right front sensor. He didn't have to do that but being the honest businessman that he is, he wanted me to know where the problem was. He also said that it is largely incorrect to assume that the ABS module is the failure point. He has told customers that the problems they were having were likely with the sensors but frequently they would insist on replacing the module. Personally, I hate replacing parts in lieu of proper diagnosis. However, in this instance, I don't have access to the VIDA/DICE tools (I tried, but everyone with a DICE and VIDA CD were out of stock...I'd have paid the $150 for the tool), so I opted for the ABS module replacement. I don't know why it didn't occur to me to look at the sensor connectors first...just human oversight I guess. In any case, Matt acted in good faith and tried to be helpful. His replacement came within a couple of days and he was very responsive to my emails. Oh, and by the way, the Rock Auto sensor ($22) worked and the light went out within 100 yards of driving and has stayed off subsequently.

The moral of the tale is to check all of the sensors thoroughly top to bottom and if you can find someone with access to VIDA/DICE, do so before replacing the ABS module. Hope this helps someone else.