ABS Sensor/speed sensor

[johnnym135x]

The ABS light is on in my 2002 Ford Explorer XLT, 6 cylinder, and I was told the rear differential sensor is bad, my question is if their are more sensors in the rear as well as the one on top of the differential and how do I replace these. And know which one is the bad one causing the problem. Brakes recently changed. Also the air bag sensor and the door ajar sensor just came on what are the cause and fixes for these aswell. Thanks please HELP!!!@!@

 

[Number4]

Just one sensor in rear. Should be one bolt to remove.
There are threads in here on both the ses light and the door ajar. I believe they are common issues with the '02 model.