Driving home tonight in my 97 Wrangler the engine died, I found a 30 amp "Engine Shutdown Relay fuse blown. I replaced it with a 40Amp fuse, and it blew too......the owners manual says nothing about it.

Anyone know what this fuse is, and what might have caused it to blow. Why do they call it a "Relay" ?

Doug Crall

There is a relay, normally mounted in the same block as that fuse. If the relay is fried, it could blow the fuse. Never replace a fuse with one of a higher rating than the circuit, thats why they use fuses rather than hardwiring them without fuses! if your 97 is the same as my 91 as far as the relays go, they are all the same and you can swap out another one with the autoshutdown one and get you home, just don't rob from Peter to pay Paul with another that is critical.

According to the Haynes manual, which is 99% useless as far as I am concurned, it's probably different. The manual does show this circuit connecting to the "Powertrain Control Module" and that module looks like it's connected to EVERYTHING.

I had no choice on the side of a busy road but to try something, or walk a long distance and get help,a fuse 30% larger is not the best to substitute, but all that was available. As it turned out, I had to use a chain and drag the Jeep back to work and leave it there then when I have a chance trailer it home to fix it somemore.

As an electrical engineer I know that fuses open for a reason, I need to find out why the fuse did it's job and opened. The Auto Shutdown relay is the path that the current followed to blow the fuse, it's probably not the reason for the fuse blowing. I am now looking for a reason it blew...anyone got an idea?

Thanks for any suggestions
doug

You've got a dead short somewhere.. you just need to ohm it out.. could be the relay or beyond it.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks Jim for the reply,

I got on line last night looking up this topic and find it is not uncommon to blow this fuse. I read where it is often a chaffed wire or melted insulation on a hot part of the engine and most common is the O2 sensor wire comming up the back of the engine, and if not that to look at any wire connected to the Engine Control Module.

When I get the PIA home and find the problem, I will post what I find, hope it helps others.

Doug

Melted insulation on the positive leads to your alternator or starter will blow it easy.

Safe way to trace it without blowing another fuse is by placing a voltometer between your + terminal and + wire and disconnecting hot leads till you find the short.Good luck, hope it's something simple.

How ya gonna do that with a blown fuse?
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

BigJim, you are soo smart. I'd have to wonder myself....

Thanks for your interest in sharing your findings. Please do let us know. We all learn from eachother here.

First thing that should touch the wires past the fuse is the relay... Or at least it would make sense to be the case... I'd go from there. I've never actually had to go out and buy a relay for my YJ, but I doubt that they would be that expencive. It would be a good place to start....

I had one once that the PLUG for the relay had went south! Parts houses sell the plugs too.. And yes they are cheap.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

I want to thank all that gave comments to my electrical problem. I want to assit others in finding their Gremlins in their Jeeps.

Having been involed in mechanical & electrical stuff both at home and work for a very long time (Director of operations & Engineering at a major TV network for 20+ years) I found usually you will find your problem related to your previous visit, or someone elses! This time it was my last time under the Jeep.

I have a Haynes Manual for the Jeep and found that the fuse that blew was the "switched" voltage that goes to the engine module. This means that "ALL" engine related devices that are on the ignition switch are on this fuse, or as you might guess could blow this fuse.

The last place I was under the hood was when I dropped the oil pan, which of course means dropping the exhaust and DISCONNECTING THE O2 SENSOR cable. It looks like I didn't get the wire back on the clip behind the rear cylinder when I put things back together. The wire eventually came in contact with #6 exhaust port on the header, the wires melted together and Blown fuse.

I was lucky, with the assistance of you guys, postings found on Google, not sure I want to credit the Haynes manual(they do make good underwear though)and a tiny bit of common sense, I found the problem in less than the time it took to replace the fuse.

Thanks all for the suggestions, I hope this helps others

Doug