I would clean the ABS sensors on the front wheels first. You can do this with the car on the ground. Turn the wheels hard to one side, take an allen key and back out the bolt holding on the sensor, gently wiggle the sensor out of the hole, clean all the metal crud off the sensor, slide it back in, tighten the bolt, turn the steering wheel and do the other side.

If the 240 has wiring connectors under the hood where the wires for the sensors clip into the main harness, I'd clean those connections, too. I know the 940 has those, I would assume the 240 does, too.

You are not having problems with an intermittent speedometer, right? That + ABS fault suggests wiring for the sensor in the diff is suspect. the rear sensor does triple-duty, sending info to the ECU, the speedo, and the ABS computer.

john