Persistent SRS fault S350

[Mercsys]

Hi all, i'm stumped with this one, so any pointers or assistance will be most welcome.

Persistent SRS fault, 220 S350 showing a 9102 fault, 220 (2002 face lift) S350 showing a 9102 fault with component R12/3.

The clock spring has been replaced as has the drivers air bag, I have also attempted to fool the system with a resistor, that did seam to work but now doesn't!

I'm handy with electronics so any schematics or component testing will be very welcome.

ty

 

[Diesel Benz]

The fault code says R12/3 resistance is too low! Are you sure the wiring is good and the new airbag has been correctly plugged in.

You could measure wiring from the SRS control unit to the airbag but I would not play with it when the airbag is plugged. Remember many of the connectors have a switch that closes wires towards the airbag when unplugged.

 

[Uky]

I have been working with Airbag/SRS systems and always approach any problem
with outmost caution...

NEVER try to measure the squib (Igniter) resistance using ordinary instruments!

The SRS uses a small continuous current to constantly test the SRS igniters.
This current is called "NoFire". When an impact occurrs, the SRS system switches to "AllFire".

Any malfunction during NoFire conditions sets an error code.

The energy level required to fire is 0.1 milliJoule, equivalent of a small pencil dropped from a hight
of about 10 cm onto a table.

Since the SRS must be functioning during a crash where the car main battery is at risk
of being destroyed, the control box is equipped with a local energy reserve.
(A bunch of electrolythic capacitors)

The normal position for the SRS box is between the front passenger seats at floor level.
That is the position that is to get crushed last...

Before performing any service to the SRS the car should be left w/o battery power
for half an hour or even longer som that the capacitors will have time for self-discharging.

What you could do is to disconnect the SRS connectors from the controller box
and then disconnect the squib in the steering wheel air bag and from there
try to see if the harness is open, shorted to itself or to chassis ground.

But that requires an exact knowledge of which cables that goes where...

...

 

[Trickythemerc]

Do you need an explosives licence to work on SRS systems ?

 

[Mercsys]

Hi all, i'm stumped with this one, so any pointers or assistance will be most welcome.

Persistent SRS fault, 220 S350 showing a 9102 fault, 220 (2002 face lift) S350 showing a 9102 fault with component R12/3.

The clock spring has been replaced as has the drivers air bag, I have also attempted to fool the system with a resistor, that did seam to work but now doesn't!

I'm handy with electronics so any schematics or component testing will be very welcome.

ty

Aaaaaaaaaaaaaaaaaaaarrrrrrrrr
Fixed it..
It seem the last time the clock spring was installed one of the connector legs fouled bending into a perfect dogleg, this explains the intermittent nature of the fault!!

 

[Mercsys]

I have been working with Airbag/SRS systems and always approach any problem
with outmost caution...

NEVER try to measure the squib (Igniter) resistance using ordinary instruments!

The SRS uses a small continuous current to constantly test the SRS igniters.
This current is called "NoFire". When an impact occurrs, the SRS system switches to "AllFire".

Any malfunction during NoFire conditions sets an error code.

The energy level required to fire is 0.1 milliJoule, equivalent of a small pencil dropped from a hight
of about 10 cm onto a table.

Since the SRS must be functioning during a crash where the car main battery is at risk
of being destroyed, the control box is equipped with a local energy reserve.
(A bunch of electrolythic capacitors)

The normal position for the SRS box is between the front passenger seats at floor level.
That is the position that is to get crushed last...

Before performing any service to the SRS the car should be left w/o battery power
for half an hour or even longer som that the capacitors will have time for self-discharging.

What you could do is to disconnect the SRS connectors from the controller box
and then disconnect the squib in the steering wheel air bag and from there
try to see if the harness is open, shorted to itself or to chassis ground.

But that requires an exact knowledge of which cables that goes where...

...

Excellent, thank you.

 

[bigjohn1]

Do you need an explosives licence to work on SRS systems ?

Explosives licences relate to the storage of the airbags. The amount of explosive is very small, but they do go well when set off!, when airbgas were introduced I worked with Ford @ Dagenham in relation to their storage regime, as they had a 'just in time' component delivery they never had many on site.