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Testing air bag circuits #

Posted by Peter Cooper on December 14, 2014, 11:07 pm

Year of Manufacture *: All years

Ive got a Citroen with an air bag light on, I cant remember the exact code but it was something like "drivers air bag open circuit".
It will be coming back in for a look next week.

I have been searching the internet and found this on Youtube.

The guy measures an air bag resistance with an Ohm Meter. I thought that doing that could cause it to explode in your face.

I thought that you were supposed to remove the air bag and put resistors into the loom in their place and then see if codes clear.

What do you think ?

.

Peter Cooper

Re: Testing air bag circuits

Posted by Rob Nicholson <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT5122' width='330' height='300' border=0 style='border:none;'> on December 14, 2014, 11:55 pm, in reply to "Testing air bag circuits"

Hi Peter,

Didn't watch the vid too late! but that is a game of roulette testing like that! Multimeters output a small voltage to calc the resistance, apparently the cheaper the meter the higher the output - you can measure it with two multimeters.

Substitution with the correct resistor in the loom is the way to go

Rob

Re: Testing air bag circuits

Posted by aidan birley <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT2879' width='330' height='300' border=0 style='border:none;'> on December 15, 2014, 8:03 am, in reply to "Re: Testing air bag circuits"

Hi

I have not watched the Video but an addition to what Rob says this is also doubly dangerous because the Air bag mechanism in unrestrained and wrong way up,

i.e. if it did trigger it would catapult the metal housing up / at operator.. A loose air bag should be stored the other way up.

Cheers Aidan

Re: Testing air bag circuits

Posted by Lee Mackintosh <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT1348' width='330' height='300' border=0 style='border:none;'> on December 15, 2014, 8:18 am, in reply to "Re: Testing air bag circuits"
Lee Mackintosh

We set of an airbag deliberatly which we'd strapped to a metal frame and the force of the explosion is unreal.

So if i was you don't test an airbag with a ohmeter just in case it does explode in your face becaue it has nothing to hold the airbag down so the force of the explosion will just fling the whole unit into the air and take you up with it.

I've seen video's where people sit on them and the foce actually lifts them off the ground with ease.

Re: Testing air bag circuits

Posted by Nick Favell <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3407' width='330' height='300' border=0 style='border:none;'> on December 15, 2014, 10:15 am, in reply to "Re: Testing air bag circuits"
Nicholas Favell

+1

Testing like this is a definite NO NO, for all the reasons stated.

Using a substitute resistor is the only way to go.

Re: Testing air bag circuits

Posted by sean savage <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT5559' width='330' height='300' border=0 style='border:none;'> on December 15, 2014, 3:27 pm, in reply to "Re: Testing air bag circuits"
Sean Savage

Totally agree with aidan. i guy a few years ago was testing exactly as you see there with airbag on the steering wheel facing upside down, the airbag ignited and LITERALLY took the guys jaw off his face!!!
sean

Re: Testing air bag circuits

Posted by Tom Williams <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT5478' width='330' height='300' border=0 style='border:none;'> on December 15, 2014, 8:59 pm, in reply to "Testing air bag circuits"
Thomas Williams

501 bulb can sometimes be used as a substitute resistor.
Although theoretical safety reasons preclude the use of an ohmmeter for checking squib resistance, does anyone have first hand knowledge of a digital ohmmeter firing a squib?
The safety aspect has to be observed, but it's a bit like the waiting period after disconnecting the battery before working on the system. At Bosch the instructors used to say wait 20 mins. Then qualify the statement by noting that there are no capacitors in the system that could retain a charge for that long.

Re: Testing air bag circuits

Posted by Nick Favell <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3407' width='330' height='300' border=0 style='border:none;'> on December 17, 2014, 9:03 am, in reply to "Re: Testing air bag circuits"
Nicholas Favell

Bosch Airbag course also says to earth yourself to the car body to dissipate any static charge that you might have in your clothing etc. before working on the system.

Re: Testing air bag circuits

Posted by Kris Gordon <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3696' width='330' height='300' border=0 style='border:none;'> on December 17, 2014, 7:13 pm, in reply to "Re: Testing air bag circuits"
Kris Gordon

Agree with above.

Try this http://www.ebay.co.uk/itm/SRS-ASSIST-RESISTANCE-EMULATOR-PLUS-AIRBAG-DIAGNOSTIC-RESISTORS-ALL-IN-ONE-UNIT-/261608780153?ssPageName=STRK:MESE:IT

Re: Testing air bag circuits

Posted by aidan birley <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT2879' width='330' height='300' border=0 style='border:none;'> on December 17, 2014, 8:12 pm, in reply to "Re: Testing air bag circuits"
Aidan Birley

Hi

Nice gadget for diagnostic purposes

I see the same firm supply these for fixing faults ...

http://www.ebay.co.uk/itm/ALL-OHMS-SRS-AIRBAG-RESISTOR-PLUG-IN-0-25W-2-AMP-FUSED-BYPASS-FAULT-LIGHT-/251653436475?ssPageName=STRK:MESE:IT

Nice to see they come with a YELLOW cable tie for a really professional repair !

This kit also has SRS simulators in it, expensive for just that but has a lot of other stuff in there to.

http://www.hickleys.com/diagnostics/hic003.php

Cheers Aidan

Re: Testing air bag circuits

Posted by Mark Robins <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3563' width='330' height='300' border=0 style='border:none;'> on January 6, 2015, 3:08 pm, in reply to "Re: Testing air bag circuits"
Mark Robins

Neat little box but if you go to Maplin you can buy a bag of potentiometers for a few quid, you can buy a box as well if you really want to be tidy to mount it in.

Mark

Re: Testing air bag circuits

Posted by Keith Simpson <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT1240' width='330' height='300' border=0 style='border:none;'> on January 6, 2015, 7:39 pm, in reply to "Re: Testing air bag circuits"

I wonder if it will work on a three wire type

Re: Testing air bag circuits

Posted by Mark Robins <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3563' width='330' height='300' border=0 style='border:none;'> on January 12, 2015, 6:52 pm, in reply to "Re: Testing air bag circuits"
Mark Robins

I found that if you stick the third wire up you nose you can smell when you got the resistance right

Re: Testing air bag circuits #

Posted by martin stackemann <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT1721' width='330' height='300' border=0 style='border:none;'> on January 12, 2015, 9:35 pm, in reply to "Testing air bag circuits #"

Just a little warning make sure it is drivers side i've had Saxo's where scanner says driver when it's in fact passenger cause the French forgot to change the software for right hand drive cars it fooled me. By the way i've had no problem checking air bag resistances 99 times out a hundred it's wiring connectors and don't they come up with some real unserviceable designs

Re: Testing air bag circuits #

Posted by Nick Favell <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3407' width='330' height='300' border=0 style='border:none;'> on January 13, 2015, 12:45 pm, in reply to "Re: Testing air bag circuits #"
Nicholas Favell

Martin, I've had the same with Renault.

I'm just very suspicous of anything French and wiring related now

Re: Testing air bag circuits #

Posted by george ambelas <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3245' width='330' height='300' border=0 style='border:none;'> on January 13, 2015, 8:50 pm, in reply to "Re: Testing air bag circuits #"
George Ambelas

using a resistor is a good practice with a 2 pin plug but there are 3 pin ones. what's the best way to go with these?

Re: Testing air bag circuits #

Posted by Tom Yates <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT2826' width='330' height='300' border=0 style='border:none;'> on February 9, 2015, 7:54 pm, in reply to "Re: Testing air bag circuits #"
Tom Yates

Two resistors, one from common to trg1 and one from common to trg2

Re: Testing air bag circuits #

Posted by george ambelas <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3245' width='330' height='300' border=0 style='border:none;'> on February 9, 2015, 8:27 pm, in reply to "Re: Testing air bag circuits #"
George Ambelas

thanks tom so one of the three wires is the ground
and the other two are triggers what is the best way to test these wires?

Re: Testing air bag circuits #

Posted by Tom yates <iframe src='https://members4.boardhost.com/ukautotalk/info/user=UKAT2826' width='330' height='300' border=0 style='border:none;'> on February 9, 2015, 9:28 pm, in reply to "Re: Testing air bag circuits #"

On some models the three pin plug replaces the two two pin plugs, one of the pins is then common NOT ground but common to the other two wires,
this maybe from the positive or negative side of the trigger capacitors in the controller, the resistance on both pyroelectric charges of the air bag are normally the same around 2.? Ohms, to test the wiring to the air bag just twist one end of each resistor together and place this in the common lead then the other end of each resistor go's into trig1 and trig2, this will substitute the airbag and if the wiring is all good the controller will see a clean system with no faults.
THESE ARE for air bag wires only NOT sensor wires, some three pin plugs on srs systems are for Temperature and Moisture Compensation on Three-Wire Capacitive Sensors

Re: Testing air bag circuits #

Posted by george ambelas <iframe src='https://members4.boardhost.com/ukautotalk/info/user=ukat3245' width='330' height='300' border=0 style='border:none;'> on February 11, 2015, 8:57 pm, in reply to "Re: Testing air bag circuits #"
George Ambelas

thanks tom you seem to know a lot about airbags can you please tell me how to identify the common?

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