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Discussion Starter #1 (Edited)
Hi,

while disconnecting the battery, I managed to make contact with the battery positive and car body with my wrench. Sparks flew ⚡💥 etc. I did have a spare battery and replaced the one in the accident.

Result (see the image below) :
With ignition to ON, all notice lights are on and I hear a fault code sound. "No Bus" displayed and -- --- for compass and temp. All gear indicators (PRND) are framed and there is a symbol (maybe a chip?) below. I do get e.g. door ajar and trunk ajar notices normally. Key fob remote does not work.

Car starts and drives normally with lights on, but no function on turn signals, speedometer, revs, gas gauge, ...

Now, did I blow a fuse (which one and where?) or the ECM (or is it ECU or PCM, i don't know)?
What can I do myself before taking it to service?
(I can use multimeter and check fuses, replace some components etc. if needed)

Any help is highly appreciated. Thank you!

With key turned to ON or driving, this is what I see:
174730
 

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You obviously didn't follow the golden rule of disconnecting the negative (ground) connection first.
Unfortunately, there is no fuse which will provide protection against a direct short to chassis of the +ve battery terminal and in this situation the large available current will find a variety of routes (not just the shortest) to the battery negative terminal. One of these routes could be via the ECM and/or other modules, possibly corrupting stored data in the process. I can't see any alternative, other than by starting to have the ECM checked by a Fiat/Chrysler/Jeep dealer with suitable diagnostic gear. As the car drives normally, the ECM may be OK and another culprit could be the Front Control Module (located just behind the screen wash filler):

MODULE-FRONT CONTROL
DESCRIPTION
The Front Control Module (FCM) is a micro controller
based module located in the right front corner of the
engine compartment. The front control module mates
to the power distribution center to form the Integrated
Power Module (IPM). The IPM connects directly to the
battery and provides the primary means of circuit protection
and power distribution for all vehicle electrical
systems. The FCM controls power to some of these
vehicle systems electrical and electromechanical loads
based on inputs received from hard wired switch
inputs and data received on the CAN bus circuit
 

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Discussion Starter #3
Well, now everything is fine again. The craziest thing...

First I rechecked all fuses and found that the one in the picture was just a bit broken. Changed it with high hopes but no effect - still "No Bus".

I gave up. I was preparing the car for service and replaced my aftermarket stereo head unit with the original one. Lo and behold: everything works just normally!

I never thought that the MyGig head unit has any special function in the electronics, but I guess it does after all. I haven't dare to change the Joying headunit back yet :)

This fuse was broken:

174734
 

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Congratulations on achieving a successful outcome!
So the only damaged module was the aftermarket radio. Was this radio connected to the canbus? ie, was radio/nav info repeated on the instrument panel and could it be operated via the steering wheel buttons? It is known that canbus problems can cause all kinds of issues, even preventing immobilser operation.
 

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Discussion Starter #5
Yes it was, via a separate module. Namely Connects2 CTSCH002 :

The nav info was never repeated, but steering wheel buttons worked just fine.
 

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I wonder if reinstalling the original REW unit caused the computers to reset connections with eachother?

Anyway great news - well done
 
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