I have 1997 XJ. The other day I was driving it with no problems and then the engine died. I found fuse #10 20 Amp yellow (Auto Shutdown Engine Controller) to be blown. I replaced the fuse and it blew again while trying to start the jeep. Has anyone else had similar issues? I put a new Mopar CPS in just to see if that was the problem but no luck. I also swapped the ASD relay for another relay and no luck there either. Any help would be great. Thanks.

 

there is a few things on the ASD relay circuit, including fuel pump relay, you will need to examine the circuit diagram by downloading the FSM.

something is short circuit, wiring around the immediate area would probably be the first thing I checked

 

Look real closely at the the oxygen sensor wiring. The PCM supplies power to the oxygen sensor heater elements through the ASD relay.

Several people have had their ASD fuse blown, to find out it was because of having a short in their Jeeps 02 sensor wires.

The ASD is definitely tied into plenty of the other circuitry which may need to be investigated. The oxygen sensor wires are just one of the more likely prime suspects to cause this sort of thing to happen. Probably it is because of the abuse they recieve being in such a harsh environment down there on the undercarriage.

 

Thanks for the info I’ll definitely look for a fsm and check the o2 wiring. Any chance there is a problem with the computer?

 

Go to cruiser54.com for a free download of your FSM.

 

Highly unlikely. More likely a short in your wiring. Blowing fuse = short. Usually, it's in the wiring.

People don't understand the PCM. It's a mysterious black box. This makes people suspicious of it, and blame all kinds of problems on the computer which have nothing to do with the computer. It's just an easy target.

They do go bad from time to time, but it's really very difficult to see how it could cause a blown fuse. Usually it's just not doing things that it should, like firing the injectors or spark plugs.

 

Usually the only thing that can fry a computer is a high voltage backsurge into it. Digital drivers use a 5v signal to switch 12v circuits to control relays, injectors, and spark coils. There are diodes in spark coil circuits to block the 40v backsurge from the coil when a spark is generated. If a diode shorts, this will fry the driver for that cylinder on a coil pack or coil-over type engine or the entire switching circuit on an engine with a single coil. Other than mechanical faults like broken solder joints or internal corrosion, there's not a lot that can cause a computer to fail. They can usually absorb a 12v short, but not anything over that.

After sitting almost a full year, the computer in my WJ failed. When we took it out of it's bracket it was covered in white aluminum corrosion and was leaking silicone. Obviously it was toast!

I would like to see the PC board circuit diagram for a PCM, but nobody seems to have one. Just curiosity, mind you. That way I could see if the blocking diodes are internal or not.

 

I have had an XJ PCM apart a few years ago. I don't recall seen any banks of diodes that would serve that function.

But since the PCM is controlling the ground side, it's very hard to see how it could be blowing fuses.

 

It's not. The problem has to be in the relay supply wiring.

 

Diagrams like those always seem to confuse me a little bit. I can kind of see what is happening with them for the most part, but I am not really sure what all of the different symbols are supposed to really mean? I am sure it would help me to understand them better if I learn those things.

 

Fuse 20 is the one giving me problems but it looks like it only goes to the PCM and ignition coil, fuse 23 goes to the o2 sensors?

 

I am curious for if someone with good electrical knowledge will interpret the last diagram.

 

Okay, so at C8 the down arrow means there is a one-way diode at that location, right? The circle above the arrow just means this diode is connected to the ASD.

Since it has a one-way diode located here at the C8.. if there was some sort of a short or electrical surge coming from the O2 sensors heater element wires, the electricity could travel and make it up to the ASD where it will sort of accumulate itself with the one-way power feed of electricity going down to the #20 fuse, to blow the fuse?

Is that something close to a possibility, for why a short within the 02 heater elements wiring sometimes blows the ASD fuses on these Jeeps?

 

Nevermind in that being a diode. I think it has to be a solid arrow...

It still may be something like that though, not sure?

 

I would think fuse 23 would blow (if the o2 wiring was at fault) but then again I don't know what that perforated line at C107 means, looks like it connects to S137 which does go to fuse 20.
????
scratching my head