My wife drove it down today and I got there 20 minutes earlier in the Tipo which I took of sorn this morning to bring here back , the garage is over 30 miles away ,they are going to look in the morning and I will update the thread later.

Well main dealer has been on the phone today to say there technician could not find the problem so he has been on to Fiat technical who say it's 99 percent certain it's the airbag ECU causing the problem which is what I suspected it was all along,however I still think it's caused by software corruption in the serial eeprom or nand flash whichever is used to store the software rather than component failure so I have asked for the old module back if it cures the problem so I can examine it,I think all this has been brought on by low battery voltage,I have known for a while the battery was on its last legs and planned to replace it just after the summer is over ,however bit late now ! As I expected this is going to cost big style but I will update the thread next week ,with the mot now run out and needing 4 new tyres there should be change out of a grand.

Well got the car back today and the old ECU , garage have only fitted 2 new front tires not the 4 as I expected they were going to do plus tracking and new MOT and the total bill came to £668.97 which was less than I was expecting to pay, or rather my wife paid !
Just got back to my workshop to examine the old ECU and as I expected there is a 32kB SPI serial Eeprom fitted on the back of the board which is what I thought may have been the source of the problem ,however on top of the board there is a huge looks to be 2700Uf capacitor which I assume holds charge so the airbag can still be fired in the event of the battery becoming disconnected in a head on crash , but the most alarming thing is none of the edge connector pins are actually soldered to the board, they just seem to be very tightly pushed fitted into a plated through hole so I am wondering now if this is the source of the problem ?
Has anyone else dismantled one of these control units ? and is it at all possible this edge connector should be hand soldered and has been overlooked at the factory ? or is it normal for the pins to be just pushed into a hole ??? Seems to be a very poor idea to me if they are not normally soldered. .

Michael Dranfield said:

Well got the car back today and the old ECU , garage have only fitted 2 new front tires not the 4 as I expected they were going to do plus tracking and new MOT and the total bill came to £668.97 which was less than I was expecting to pay, or rather my wife paid !
Just got back to my workshop to examine the old ECU and as I expected there is a 32kB SPI serial Eeprom fitted on the back of the board which is what I thought may have been the source of the problem ,however on top of the board there is a huge looks to be 2700Uf capacitor which I assume holds charge so the airbag can still be fired in the event of the battery becoming disconnected in a head on crash , but the most alarming thing is none of the edge connector pins are actually soldered to the board, they just seem to be very tightly pushed fitted into a plated through hole so I am wondering now if this is the source of the problem ?
Has anyone else dismantled one of these control units ? and is it at all possible this edge connector should be hand soldered and has been overlooked at the factory ? or is it normal for the pins to be just pushed into a hole ??? Seems to be a very poor idea to me if they are not normally soldered. .

Click to expand...

Hi,
I can't see your pictures because works IT system blocks them. There are solderless connector to PCB terminations out there and they seem to be pretty reliable. I've seen them used on very high density connectors used in telecommunications kit. They are multi-contact. sprung and barbed. They are hard to remove. The main reasons for using them are reliability and to avoid through hole soldering on a otherwise surface mount PCB (cost reduction). Arguably they are more reliable than solder as they can move very slightly to relieve any stress caused by the mating connector whereas solder won't move and the stress can crack the joint or PCB trace.


Robert G8RPI.

Hi,Robert, sorry about the delay in replying,only just come back off holiday,many thanks for your reply,I have never come across this non soldered contact before but you live and learn.

Hi @Michael Dranfield
No problem. I can confirm that the connector shown in your photos is the solderless type.



Robert.

I had the same issue recently (spontaneously broken Airbag module, both driver and pass lights on, Fuel Cutoff unavailable and warning triangle in the dash).
I have read the car with MES….Body ctrl module cannot see/communicate with Airbag module. If your OBD scanner cannot access Airbag module (do not confuse it with Body ctrl module), story that follows may apply to you as well.
Bottom line, it is broken Airbag module, more precisely broken power supply in the module. I have opened it and compared it on the bench with properly working replacement (connected standalone to my OBD scanner via MES software)
Big elco cap 3200uF (supply backup cap) in the middle should show 32 Vdc…on the broken module it is 11,x Vdc. Other regulators that generate 5V and 3.3V for the rest of ICs….generate 0V on broken unit.
All regulators come from a custom IC…ATIC99-C4 (A2C00059303)…, which is fed from 12V battery pin on the Airbag module (verified that 12v reaches ATIC99-C4) . There are no fuses in the Airbag module supply.
I cannot find data sheet of ATIC99-C4, but could order replacement part…as I intend to replace it anyway (though it will be tough, 80pin device in QFP80 package).
Finally, the simplest way out is to order the same part number from a scrap car, crash free unit, (in my case it is Airbag module 51897787). It is plug and play replace (may even not need a proxy alignment).
Another Fiat enthusiast told me that these Airbag modules often die if you have weak car battery that dives under 12V at start…stressing somehow power supply chip ATIC99-C4.