Most places will tell you to try to track down each abs speed sensor connector, but really, you can just check all sensors right at the ABS computer module. To get to this module and plug only takes removing 3 half turn screws. With a multimeter you can check resistance on connector pins: 4 and 6 for LH Front ABS speed sensor 21 and 11 for RH Front ABS speed sensor 8 and 9 for LH Rear ABS speed sensor 24 and 26 for RH Rear ABS speed sensor The resistance should read about ~1000 ohms across all sensors, some deviation is okay, but normally a failed sensor will be substantially different than the others.     Consider also replacing all ABS relays for best longevity: E30 ABS Pedal pulsating at idle problem