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Old 25-06-2018   #16
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Re: Punto evo airbag light on.

Another perculiarity I see ,on the evo there are 2 sets of wires under the seat 2 for the seat belt stalks which operate ok ,so that leaves the other loom a of 3 wires,now given the evo has airbags in the seat side I can only see one possible configuration for the 3 wires and that is seat occupancy sensor switch and air bag trigger with a common ground or earth, however when I meter the 3 wires one pair is short circuit, zero ohms no matter if the seat is occupied or not and the other pair measures infinity, now logic would tell me the seat occupancy sensor is stuck down but the passenger seat gives the same reading so it seems a bit unlikely both seats are faulty, I can't make any comparisons with the Grande punto as there are only 2 wires due to no seat airbag.
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Old 26-06-2018   #17
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Re: Punto evo airbag light on.

Quote Originally Posted by Michael Dranfield View Post
Many thanks Robert but I don't think e learn for the grand punto will help with the evo because I have a Grande punto as well and I have made some comparison checks between the two cars ,on the Grande the seatbelt stalks micro switch are normally open but on the evo they are normally closed.
Does the GP have the Continental airbag system? The GP has two different systems and eLearn covers both. If it's the same series ECU I doubt the power pins have changed.


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Old 26-06-2018   #18
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Re: Punto evo airbag light on.

I don't know as I have taken the scanner back now but I can't get out of my head with 3 wires to the seat how can 2 be zero ohms no matter what you do ? And both seats read the same,surley both seats could not have gone faulty at the same time ????
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Old 26-06-2018   #19
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Re: Punto evo airbag light on.

ok so just had a look on the internet while eating my dinner researching what part the front seats play in the airbag system and it would seem I have solved the mystery of the short zero ohm reading on the seat connector ,a special type of plug and socket is used with a built in shorting bar which as soon as the plug is detached from its socket puts a dead short across the airbag trigger wires so when the airbag is removed there is no danger of it been accidentally fired by a charge of static electricity.
As for the seat occupancy sensors having an infinite resistance reading the snap on scanner said both seats are working so it could use a capacitive pressure sensor rather than a restive one and in this way the system can determine how the occupants are placed in the seats.
All clever stuff but unfortunately my new found knowledge on SRS systems is all immaterial now as the car is booked in the mainstealership tomorrow for evaluation but my conclusion is one of two things either it needs a software upgrade or the airbag ecu is faulty.
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Old 27-06-2018   #20
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Quote Originally Posted by Michael Dranfield View Post
ok so just had a look on the internet while eating my dinner researching what part the front seats play in the airbag
All clever stuff but unfortunately my new found knowledge on SRS systems is all immaterial now as the car is booked in the mainstealership tomorrow for evaluation but my conclusion is one of two things either it needs a software upgrade or the airbag ecu is faulty.
Well.. what did they discover?
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Old 27-06-2018   #21
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Re: Punto evo airbag light on.

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.
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Old 29-06-2018   #22
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Re: Punto evo airbag light on.

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.
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Old 04-07-2018   #23
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Re: Punto evo airbag light on.

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. .
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Old 04-07-2018   #24
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Re: Punto evo airbag light on.

Quote Originally Posted by Michael Dranfield View Post
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. .
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.


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Old 14-07-2018   #25
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Re: Punto evo airbag light on.

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.
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Old 15-07-2018   #26
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Re: Punto evo airbag light on.

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



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