Rough_Cherokee2002

Hello, my 1997 Cherokee Country has been randomly blowing the 15amp fuse that is marked as 11 and 12 on my wiring diagram. There is no pattern to when it blows. Im still not completely sure as to where my junction block is so even just figuring that out would be a great help. I have had this problem on and off for about a year now. It ceased all summer and just now came back. Yes, I use my cherokee in the mud but it is also my daily driver so i dont beat it up too badly so i don't think it is something caused by me pushing it too hard. I have an aftermarket radio but everything else is stock. I have had a mechanic look at it multiple times in the past only for the problem to continue after a few months with a new ECM (last resort). I am at a loss on what to look for or what to do so all help is greatly appreciated. It is a 1997 Cherokee Country with 197k miles.

odie64

The first check would to see what items are on the circuit for that fuse. (blower motor, rear window defrost, cigarette lighter /12 volt power outlet …) and then make a mental note of what items were on( lights, wipers, blower motor …)when the fuse blows next. I would then look at the higher draw items on the circuit as the most likely cause for the fuse failures. A blower motor or wiper motor with worn brushes can draw more amperage than the same new part. With it being random it is most likely a combination of several loads on the system with one or more drawing more amperage than normal.

PatHenry

^^^^^ This.

odie64

I would advise to seek another mechanic. The ECM is a low amperage unit typically using 5 volt reference signals. and then uses relays to control higher amperage circuits. In my 30 years in the automotive field I can not ever remember replacing an ECM to solve a random fuse failure issue.

jordan96xj

For 97:

15amp at position 11/12 is Fuse 21 for the power side (not the switching side) of the Fuel Pump Relay.

So first check the condition of the fuel pump connector, and ensure that it is not beginning to melt (and causing a short that would blow the fuse). Then you probably want to test the amperage draw that the fuel pump is creating, as it may be beginning to fail. Or the wiring inside the tank to the pump itself might be starting to have problems and creating a short circuit there (which would also blow the fuse).

Also, a mechanic that replaces a non related PCM for a blown fuse that powers the fuel pump should not be your mechanic. Perhaps he blew your PCM by doing a bad fuel pump current draw test, and made you pay for it. Don't know.

jordan96xj

Here is a video for easily testing current draw on a fuel pump using the fuel pump relay and a meter (for a different vehicle, but the concept is exactly the same). But if you do this yourself, please ensure that you know how to use your meter and select the proper pins of the fuel pump relay to do the test on. If you use the wrong sockets on the relay, you will send battery voltage directly to the computer, and likely fry it. So it is an easy test, but it must be done correctly and with care.