I found a replacement ABS/STC module at a dealer with a great price, $540 compared to $700 at other dealers. I planned to replace and pulled the module. I opened it up with a dremel tool. The circuit board looked fine. There was a solder issue with the Quad Flat Pack in the center. Being an SMT solder engineer, I cleaned the QFP that must have removed a solder short. That part looked like it was soldered on in a separate process (poorly) where the rest of the board looked good. The board was built in Malaysia. I reassembled the module and now for 2 weeks, no error messages have come up. I see the ABS reacting and signalling function when I turn fast or spin out intentionally. Glad I didn't pay the $800 to replace a defective part. How many times has this happened, that defective parts are replaced at a high cost, when the part has a defect that is intermittent? Thanks Volvo...

There is a guy on eBay charging $125 to repair the unit. He opens them up and "fixes" them. The people that have used his service are happy with spending $125 vs $800 with labor.
This reminds me of poor soldering with the fuel pump and overdrive relays on 200/700 volvos, and folks started resoldering them and they worked just fine.
Thanks for the update and I just hope that more bricksters on this board, begin to take the ABS unit apart and resolder it and post results here on their success or failure. This is the only way to spread good information around.

If you have pictures of what you found and what you did, please repost with a catchy title so that more people on this board are aware of what you did.
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'88 240, '92 740, '98 v70 GLT John in Tampa Bay