Why is your abs light on in your 2000 Isuzu Rodeo?

This problem is typically caused by a bad differential speed sensor that can be easily replaced by your mechanic for about $300 ($200 for parts, $200 for labor). If you are mechanically inclined you can fix it yourself for about $100 in parts from the Arizona Autohaus web site. After fixing it you will need to calibrate the speed sensor in the following manner:

http://www.automotiveforums.com/vbulletin/showthread.php?t=193043

The owners manual states stop the car immediately. Shut it off, start it up again and for about

quarter to half mile do not exceed 8 mph, go slow and the light will shut off. If the light comes back on,

repeat the same. If it does not go off or it returns, have it serviced.

<jhoover58> Someone edited out the rest of my answer, I've added it back here. There is one additional problem that many mechanics can't find. That is a wire has broken between the abs brake module and the speed sensor on the differential. Unplug the abs module and speed sensor connection then perform a continuity test on each wire. If you find a bad wire, splice in a new one to see if the light goes out. That fixed my problem but not until I had already spent $300 on a mechanic who at the end said I needed a new abs module, a new complete wiring harness to go along with the new speed sensor he put in that didn't fix the problem. I also spent days searching elsewhere for the problem. I wish I knew about the bad wire problem earlier.