I have a 15a fuse in the block under the hood that blows as soon as you turn the key on. I have asked my local Jeep dealer and he did not know what the fuse was for . I am posting a picture of the block with the fuse. Any one have any information would be a big help.

Thanks Howard

 

Oxygen Sensor Heaters.

 

Sometimes it's good to have a hard failure; makes it somewhat easier to find the problem.

Assuming you don't know this already:

First, inspect the upstream O2S wiring as it passes over the intake manifold for chafing. Then inspect the downstream O2S wiring for chafing and in each case, exposing the O2S heater power wire to the chassis.

Next, detach, in turn, each O2S harnes connector, each time turning the key to run. The one that still blows the fuse is at fault. The one that is suspect needs to be examined more closely.

Get this far and I will help you with wiring diagram data.

 

I blew that fuse last week. Like CCKen said...it was my upstream o2 sensor.

 

That is great information, tomorrow I am taking the jeep to my friend that has a lift to replace the shocks, while their I will trace out the o2 senser.
I would have been lost without your help.

Thanks
Howard
1999 cherokee 4X4 4.0

 

All fixed the oxygen sensor was bad.
Cant thank you enough..

 

Glad to help a fellow Ninty-Niner out.

Cheers