Fiat 500 Electrical Nightmare – BCM,Wipers,Lights,Hatch

Fiat-Cropped

This is the story of a 2012 Fiat 500. It presented with No wipers front or rear. The car also had a couple other strange intermittent issues we’ll get to later.

The story begins.

This car came in with no wipers front or rear. It also had intermittent hatch release problems, and license plate lamp going out. What I found ended up being one of the coolest fixes I’ve ever had to do on a car. 

After wasting a little time testing the wiper motors they both appeared to work. They were both acting very strange though getting 12v power all the time. It wasn’t enough amps though to power the motor but make them buzz very very slowly moving around their loop. Even when the switch was off the wiper motors continued to buzz and rotate very very slowly. 

I got into it a little bit more and found all these messed up wires in the hatch jamb. Just about every single wire was cut or damaged.

Do not cut the boot. Instead remove the panel from the hatch and unhook all the connectors so you can snake the wire out. After you disconnect everything and pull the wire out you can slide the boot down the harness and make your repairs. 

I don’t have a picture after I repaired them, but just spent some time soldering them all back together and heat shrinking them all.  I really thought for sure that repairing these wires would fix all of the problems. Boy was I Wrong!

Hatch Wiring

fiat messed up wiring
Fiat messed up wiring

When I was removing the wiring out of the hatch I found some more problems in the harness. The connector on the license plate lamp / hatch release button was badly corroded. The connector that plugs into it, and the connector in the light were trashed. I didn’t wanna buy a new assembly just because of messed up wiring. There was just enough room on the wires to get in there and solder a new connector on. So while I was in the trunk repairing the other wires, I soldered a new connector to the license plate lamp /  hatch release assembly, and a new connector on the body harness to plug into it.  

Release handle / License lamp Harness

Hatch/Lamp Harness
Hatch/Lamp Harness
Repaired Harness
Repaired Harness

Well that should take care of it right? That’s what I thought.

After repairing all the damaged wiring in the hatch everything was fixed but still no wipers, front or rear. The intermittent problems with the hatch release and license plate lamp were fixed.  Back to the diagnostics. 

Looking at the wiring diagrams I can see that the wipers go through the body control  module. So after a little bit more diagnostic  I’m quite confident the problem is in the body control module (BCM). 

Since the wipers are operated by a MUX switch instead of a normal kind of open/close switch, there is no way I can easily  bypass the body control module.

I know the motors work, so my options are to wire up a relay and switch right to the motor so at least it will have wipers. Ideally I would use the factory switch and just wire my relay to that but since it uses a multiplexer style switching there is no way to feasibly do that. I would have to wire it up to a external aftermarket switch somewhere and I really didn’t want to do that. 

The other option is to replace the costly body control module (BCM). We went for this one. Replacing the BCM Requires the dealership to reprogram it otherwise the car will not run.

Wiper Diagram

Fiat 500 Wiper Diagram
Fiat 500 Wiper Diagram

Hatch Release Pinout

Hatch Release / License plate lamp harness
Hatch release actuator harness
Hatch release actuator harness

First I called the local Fiat dealership to ask them if I could put in a used BCM, and then bring it to them to have programmed. 

They assured me it was no problem and gave me a reasonable quote to do it. 

I went on ebay and bought a used body control module and installed it in the car to confirm my diagnosis. The wipers worked everything was fine. However I couldn’t start the car without having it reprogrammed… So for now put the old one back in.

We called back the local dealer and again told them what we were doing and asked if they could reprogram the BCM for us. They told us no problem, we setup an appointment to drop it off.

So we drove the car there and i actually swapped the new BCM into the car in the parking lot of the dealership. The service adviser came out and I explained what I had done and again was assured no problem and we left the car.

Few hours later they call us and say they cannot reprogram a used BCM, that it has to be a new virgin BCM to be able to reprogram. So after they already confirmed for us 3 times that they could reprogram a USED BCM they tell us we can’t. 

So I go back swap the old one back in in the parking lot and now we are right back where we started minus a hundred dollars for the ebay BCM.

Ebay BCM

Fiat 500 BCM
Fiat 500 BCM
Fiat 500 BCM
Fiat 500 BCM

I wasn’t ready to give up so I decided to open up the BCM and take a look inside. Opening this thing up in itself was a chore and I don’t have detailed instructions to open it. Jut get a bunch of small flat blades and go to town on it. 

Really I just wanted to look for anything obvious and got extremely  lucky. I easily spotted a blown chip. After looking up the part number found out it was a Motor controller/bridge and knew it had to be the wiper motor but it was still a guess. 

 

Luckily I had one of those same exact motor controller chips right in my pocket. Just kidding, I used the worthless paperweight of a BCM that I got off ebay, and desoldered the chip. I’m gonna attempt to replace the blown chip with the one from the ebay BCM. Still am not 100% sure what that chip even does but figure its worth a shot. At this point I was ready to buy a new one anyways and was just hoping for the best. But if I mess this up the car wont even run anymore so I definitely had my fingers crossed.

Being very careful I removed the blown chip from the original BCM.

Blown Chips

Fiat 500 Blown BCM
Fiat 500 Blown BCM
Blown Chip in BCM
Blown Chip in BCM
Removing Blown Chip in BCM
Removing Blown Chip in BCM

Now that I have the bad chip carefully removed from the original BCM, and the replacement chip from the ebay BCM we are ready to begin the final step.

The Fix!

BCM Bridges
BCM Bridges

The final step was to solder the replacement chip very carefully to the original BCM.

 

And after all this the wipers finally worked!

I hope this helps someone else with their FIAT 500 Electrical Problems.  There are relays on here for the headlights that can blow. So if your fiat has a headlamp problem because of a bad BCM you can likely fix it in a similar fashion.

Soldering New chip to BCM
Soldering New chip to BCM
Soldering New chip to BCM
Repaired BCM Done!
Repaired BCM Done!

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