The ABS/Trac light is on because you have a problem with that system, you need to have the codes read with a scanner that reads "C" codes...you can tets the sensors and ring gears with a volt/ohm meter, unplug a sensor, measure the resistance across it with the ohm meter, it should read 800-1400 ohms, then switch to volts, spin the wheel and it should produce voltage...the rest of the system requires the scan tool.