COM2000 / Air bag fault / testing

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RichardW
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COM2000 / Air bag fault / testing

Post by RichardW »

My Sister's 02 Xsara again...

Air bag light on, and Lexia reports fault with drivers airbag level 1 igniter. Now, I am pretty sure it will be the COM2000 unit, as that is the most likely place for it to break down. But, is there anyway of testing? If the bag and unit are disconnected, would a multi meter show up a failed cable on a continuity / resistance check? Could I stick a resistor across the unit input side to see the light goes out (what resistance?) and then the same on the output side with it reconnected to input side to see it comes back on?
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Re: COM2000 / Air bag fault / testing

Post by miked »

I have no idea what resistance the igniter should be however..

Be careful if you try checking continuity / resistance of the airbag igniter. To measure resistance your multimeter will have to pass current through the circuit. I guess the voltage varies depending on the type of meter and I have no idea how much current the igniter needs to set it off.

I would presume it would be more than a normal meter would supply in resistance check mode but I wouldn't test the theory unless you are told it definitely will be safe to do so.
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Re: COM2000 / Air bag fault / testing

Post by RichardW »

Ah, I wasn't thinking of putting a voltage up the ingiter - just trying to measure the continuity across the COM 2000 with the bag disconnected. I'm not completely suicidal.... :-D
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Re: COM2000 / Air bag fault / testing

Post by BX »

The resistance you will read depends on the quality of your ohm meter and how well and reliably it zeros. The actual resistance between the connector on the rear of the com switch and the airbag connector is less than one ohm. As you probably well know there are 2 connectors on the rear of the switch which are joined to the 2 airbag igniters via some lengths of bus bar and ribbon cable. I recently repaired one. The ribbon cable was cracked where it is bonded into the centre spool. I pared away some black plastic, stripped the insulation off the damaged part and soldered over the crack in the copper ribbon. I then insulated and secured all with hot melt glue.
When reassembling it is important to wind up the coil of ribbon cable fully and then unwind it by about 2 turns to the point where all lines up again. Too much and the cable can flex too much on left hand turns, too little and a tight right hand turn will snap the ribbon.
A 2.2ohm resistor can be as a dummy ignitor and can be inserted at various points to locate the fault if required. Beware many of these faults can be intermittent.
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