I have a 99 Cherokee with a high voltage code for my 02 sensor, I changed it an my engine light is still on. What else can it be

 

which o2 sensor? you have two.

 

Sensor 1 bank 1

 

This may seem like a stupid question, but did you reset the code? It doesn't go off by itself.

If that's not it, check the O2 heater circuit fuse in the PDC under the hood. I don't know what position it's in for a '99, but if the fuse is blown, it will throw the code again.

If you already replaced the O2 sensor and the fuse, and it's blowing again or still showing a code, look for a chafed or broken wire and/or refresh your grounds. Look for where the wire might have rubbed up against something and damaged the insulation.

I just went through this crap with my 2000. It kept blowing the B1S1 heater circuit fuse with a brand new O2 sensor in it. I finally gave up and took it to a shop. They messed with it for two hours trying to find the source of the problem. In the course of shaking the wires trying to find it, they got it to stop blowing the fuse and then couldn't get it to blow again. So now I'm not throwing a code, but I can't help but feel I'm on borrowed time until it decides on its own to start up again.