There's a known issue with this generation of ABS controllers where they had "cold" solder joints on the PCB inside the controller housing causing intermittent open circuits. Another common issue is the wheel sensors misreading due to dirt, grease, etc. building up on the sensor tip. These failures are more common in the salted areas for obvious reasons. Until you have someone scan the ABS module for codes, you're gonna be shooting in the dark. So, start first with what you can easily check. Pull the wheels and closely inspect the wheel sensors, harnesses, plugs, etc. Make sure the sensors and reluctor wheels are clean.