Airbag Diagnostics

Talk about the 406's electrical system, what wires do what, how to add extra functionality, etc.

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benmack
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Posts: 8
Joined: Wed Sep 28, 2011 10:02 am

Airbag Diagnostics

Post by benmack » Wed May 09, 2018 5:28 pm

I've had a good read of various airbag threads on here, not found my answers yet so hope you don't mind a new thread...

I have a 2004 406 exec, airbag light on constant, local garage diagnostics say driver side trigger, so I'm assuming the squib or com2000 module. Couple of questions:-

a) to check if this is the problem, can I simulate the trigger by disconnecting the airbag connector from the back of the com2000 module, and connecting a resistor across it? I've read a 3.3R 0.25W resistor will do. If so, any pointers as to which the airbag plug is?

b) given the light is steady I assume the fault has latched and the airbag ecu will need resetting to see if I've fixed it - can this be done without a PP2000 diag tool? I've seen various posts about resetting the BSI by sequence of switching on igntition, lights, etc, just wondering if a similar procedure is available for the airbag ecu?

Thanks in advance :D

benmack
Newbie
Posts: 8
Joined: Wed Sep 28, 2011 10:02 am

Re: Airbag Diagnostics

Post by benmack » Fri May 11, 2018 11:14 am

I've sorted this, thought I'd post a few tips in case it helps others.

The problem turned out to be an intermittent contact in the connector on the back of the com2000 module. I did the following:-

I bought a PP2000/Diagbox adapter https://www.amazon.co.uk/gp/product/B078Y46K9J/ so I could read and clear codes. This is a generic chinese copy with fake labels, works OK, you can get it cheaper on ebay but I needed it in a hurry. The software on the DVD is the standard psa diagbox, with upgrades to 7.83, but is a nightmare to install. I installed it on an old XP laptop, following the video on the DVD. It throws lots of errors, and I had to go through the whole installation and upgrade procedure twice before I could get it to work, took many hours. However from what I've read this is typical of PP2000/diagbox, and not specific to the software supplied with this product. I could not find a free download elsewhere so had to use the DVD. Shout if you want a copy.

I removed the cover under the steering column, unplugged the two airbag connectors (bottom left blue is trigger 1, and right brown trigger 2), and checked I got faults on both trigger 1 and 2. I then fitted 3R3 bypass resistors to both connectors - this allowed me to clear the permanent faults using PP2000, proving that this was the problem. Here's a useful video showing the connectors, and discussing the 3R3 bypass resistor trick https://www.youtube.com/watch?v=l8E2-0OG-BI

I measured the resistance across the trigger terminals on the back of the com2000, both 3R3, even when turning steering wheel, so no problems with squib or com2000. I used a digital multimeter, and slid piece of plastic up side of pins to disconnect the safety spring that shorts the pins when unplugged. There is lots of scaremongering about doing this, but I do not believe the few uA from a digital multimeter can trigger an airbag, and this video from an airbag specialist seems to confirm it is safe https://www.youtube.com/watch?v=uAklUlvAIrs

I then removed the bypass resistors, gave connectors a good clean with solvent, reconnected, and measured resistance across crimps in back of connectors (with car battery disconnected, should measure around 3.3R), all good.

I cleared faults from ecu again, now all sorted :D

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GingerMagic
3.0 24v
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Joined: Fri Apr 06, 2012 9:02 pm
Location: Bournemouth

Re: Airbag Diagnostics

Post by GingerMagic » Fri May 11, 2018 12:37 pm

Good work :cheesy:
As you said the newer cars have a trigger 1 and a trigger 2 and to be honest it's normally the connectors on the airbag itself that cause problems, so well done in using the Comms connection instead.
As you have PP2000, it's possible to simply mark the airbag as 'absent' which will turn off the light on the dash but obviously render the airbag useless.

On the 406, most issues can be sorted with a dose of contact cleaner..... :wink:
1999 T4 family wagon, slow as a turd but the kids like it
2002 Citroen Xsara Picasso Hdi90 - Dirtied by the kids, Dented by the wife....
Sadly sold the 406, best cars I have ever owned
PP2000 user, can help with faults / diagnostics in the Bournemouth area.

benmack
Newbie
Posts: 8
Joined: Wed Sep 28, 2011 10:02 am

Re: Airbag Diagnostics

Post by benmack » Fri May 11, 2018 12:55 pm

Thanks for the comments. I tried marking the airbag as absent, but this caused a "misconfiguration" fault and the airbag light stayed on

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