Technical The dreaded SRS lights

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Technical The dreaded SRS lights

Aura

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Hey folks! Happy new year to all of you!
I'm a newbie (very much so), so apologies in advance if I ask silly questions or if this was previously posted - I've been reading these forums for weeks and weeks, couldn't find my answer so I decided to post.

I have a punto evo 1.4 petrol, reg 60 - I haven't used it much this year for obvious reasons, after being parked for about a month, I took it for a 10ish mile drive one day in October, all good, started first time. I parked it up, done my stuff, returned home.. I don't know at what point on my return, the airbags lights came on (both driver and passenger) along with the seatbelts, generic triangle error, milage blinking and 'fuel cut off unavailable' - the usual.
It's worth mentioning it was raining pretty bad and I hit a speed bump quite hard cause I didn't see it (my bad!), so initially I thought a connector under the seat came off.

I left it parked for another month cause I didn't have the time to look at it - I started checking things over the last month only. Here's what I did:

- Battery check: after being parked for so long, the battery went a bit down, it was 11.50V - I charged it off some leads from my friend's battery and brought it back to 12.7V (engine not running).
- Removed the stop/start sensor, removed the negative, shorted it with the positive, left it OVERNIGHT (I keep seeing on youtube that people remove also the positive(s) and short them, but I don't understand why? I thought, the battery is out if I remove the negative, so why bother removing the positive also? But if you can shed some light on this - much appreciated), connected it again the following day, negative first, then stop/start: no luck
- Ensured the connectors under the seat were plugged in, disconnected them, reconnected them
- Removed the plastic cap under the seat (on the foot rest) - both sides. Unplugged the connectors and plugged them back in again - now, they're wrapped in electric tape, from what I see the male connector has no broken cables, I unscrewed the female from the foot rest and looked underneath, it has a plastic cap and the cables are again wrapped in electric tape, I didn't bother checking any further but it seemed good and sound)
- Since I could not find the fuse responsible for the SRS stuff (it seems a secret of Fatima, I read), I decided to go ahead and test ALL the fuses in the engine box and also in the glove box - all good.
- Got ahold of a OBD2 interface with yellow cable, purchased multiecuscan, gave it a scan. MES found only the modules for body, and 2 dashboard modules (CTM and another one I don't have at hand but I can find if needed).. No airbag module. On the body module I had the FIS sensor error, proxi alignment error (unsupported component) and U1726-87 Airbag node missing message.
The dashboard CTM/Blue and me showed no errors. The other dashboard module I don't recall had again U1726-87 no communication with airbag ECU.

I reset all of them, they all clear temporarily apart from the airbag U1726-87. When I start the car again, they all come back, of course :'(

So my understanding of this is:
- The Airbag computer is not talking at all: missing voltage supply? bad cable? busted ecu? who knows!
- The FIS sensor comes up cause it needs that airbag ecu
- Odometer blinks cause it requires a proxi realignment, because the car expects an airbag sensor that it cannot find
Just my n00b guesses here - input appreciated.

I rang a local FIAT dealership (north London), they quoted me 650 for the airbag ecu replacement including labour. They have however suggested that if my diagnosis is incorrect then that's it - money wasted, they suggested another 125 on top to give it a scan (whoa..) so they will be 100% sure if that's the airbag ECU.
I have the feeling though, that their scan will give them pretty much the same results, they will suggest replacing the airbag ECU and it may or may not fix it really - plus, if I just lost an earth on the sensor, they'll just tell me they've replaced it and charge me a fortune for that regardless.

So the first question I have for you is:
- I am unable to find the location of the airbag ECU, does anybody know where it is or can point me to some video/link/article/whatever other resource?
- Any additional check I should be doing?
- Is it worth faffing? Should I just take it to FIAT instead?
- Or.. anybody here who has a trusted person non-FIAT? My mechanic seems a bit clueless about all the ECU stuff, I could take it to an autoelectrician but I have the feeling that unless they really know FIATs very well, it'd be wasted money.
- I could get a new battery and probably will, however I don't think it'd be the battery - but what do I know? :D


Worth mentioning, I had the same experience with the stop/start sensor till I decided to give up on it, 5 mechanics and autoelectricians, non-FIAT, nobody had a clue - I don't want the stop/start anyway so it wasn't a big deal :) But this one will fail the MOT so I kinda have to fix it.

Apologies for the long wordy post and thanks in advance to whoever read it till the end :)
 
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