2003 e46 318ti compact sport airbag light

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  1. 2003 e46 318ti compact sport airbag light 
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    Hi all, just wondering if anyone can help?! I'm having problems with a re-occuring airbag light. i took it yesterday to a garage who ran a diagnostic check for faults however he said that none were showing, ie pressure pad, loom etc.. But he did write something down for me saying that the problem was 'resistance too high, sporadic fault not currently present, frequency 1 logistics 1?! the diagnostic machine was autologic equipment. He reset the system and the light went out however has appeared again today. Any help would be appreciated. Thanks in advance.
     
     

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    wtf is it with all the big writing man

    Alpine white
    19" black type1 MUTECS
    ONE OF A KIND
     
     

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    Anybody?!
     
     

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    Hi I did a search and found this-
    There have been a few posts recently regarding the airbag light being on due to faulty occupancy sensors and the fitting of a bypass box, I've done a bit of research and put together the information I've gathered.

    I'm in no way recommending the fitment of a bypass unit for a vehicle used on the road. I don't sell them so have nothing to gain, I've gathered and posted this information out of interest only. Hopefully the information provided below will allow owners to make an informed decision regarding fitting a bypass box, at least if you have read this post and decide to go ahead you will understand the implications. This information relates to the E46 models and may differ for anything else.

    Q. What is an occupancy sensor?
    A. It is a mat with an integrated electrical circuit installed into the front passenger seat base which detects when a person sitting in the seat.

    Q. Does the drivers seat have one?
    A. No.

    Q. What's the idea behind it?
    A. The idea is that if the front seat is unoccupied in the event of an accident the passenger airbag will not deploy, thereby saving on repair costs.

    Q. How does it work?
    A. The mat is pressure sensitive, it has 2 wires coming from it. It can be thought of in simple terms as a switch – If a person is sitting in the seat then the switch is ‘on’ otherwise its ‘off’.

    Q. Ok, if it’s just a switch, when it breaks why can’t I just join the 2 wires together and clear the fault codes?
    A. It’s a bit more complicated than that, there is some crude intelligence built into the mat. During the system check at start up the electrical resistance through the mat is measured. If the resistance is found to be out of a predetermined range then a fault is detected and the airbag light is switched on.

    Q. Why do they become faulty?
    A. The mats seem to be fairly fragile and if you frequently carry a passenger then the mat will get a hammering. When they break the sensor will either give a short circuit (no resistance) or an open circuit (infinite resistance).

    Q. Are the mats repairable?
    A. Not unless there is a break in the external wiring which is rare.

    Q. What is the operational state of the SRS system (airbags and seat belt pretensioners) if the occupancy sensor is faulty and the airbag light is on?
    A. There doesn’t seem to be a definitive answer to this question. I’ve personally spoken to 2 BMW technicians from different dealerships and they both said the whole SRS system is disabled when the airbag light is on (this could well be an official BMW response though). Other people say that the system is intelligent enough to work out where the fault lies and activate the airbags which haven't returned a fault. Another view is that all the airbags will still attempt to be deployed in the event of a collision.

    Q. How do the bypass boxes on ebay work then?
    A. The bypass box just contains a simple circuit with an electrical resistance in the same range the mat gives when a person is sitting in the seat.

    Q. Will fitting a bypass prevent faults from other areas of the SRS (airbags and seat belt pretensioners) system being reported?
    A. No, the same system checks are carried out at startup and faults in other areas of the system will switch on the airbag light if a problem is detected.

    Q. How do I fit a bypass sensor?
    A. Disconnect the negative terminal from the battery, wait 30 mins, fit the sensor under the passenger seat, reconnect the battery, clear the fault codes from the airbag module to extinguish the airbag light

    Q. Disconnect the battery? Won't that mean I'll need the radio code? Will it upset anything else?
    A. It didn't on my 2003 E46, the radio code is stored in the ECU so after reconnection apart from reprograming the radio preset channels you should be good to go.

    Q. What about using a child seat in the front of the car, how is this affected?
    A. The owners manual (page 53) states that no child restraint system should be used in the front passenger seat of the car anyway so the situation remains the same.

    Q. What are the pros to bypassing the occupancy sensor?

    * It's cheaper and quicker than replacing the mat in the seat.
    * The bypass unit will reactivate the airbag system (if it's even disabled in the first place)
    * The occupancy sensor fault will not reoccur.
    * The airbag light will be extinguished and free to light up for other faults in the system.


    Q. What are the cons to bypassing the occupancy sensor?

    * It isn't the proper fix for the problem.
    * You are fitting a part which is not approved by the manufacturer.
    * You are changing the operation of a safety system.
    * If your vehicle is involved in an accident, the occupants are injured and the bypass is found your insurance will be invalid and you will more than likely be prosecuted.
    * Knowingly selling the vehicle on with a bypass fitted without informing the buyer is morally VERY wrong.
    * The passenger airbag will needlessly be deployed in an accident if you aren't carrying a passenger.


    Q. Are there any situations where its acceptable to fit a bypass unit
    A. Probably, for instance if you have a track car and swap your seats for bucket type and there isn't room in them for the sensor mat.

    Q. Where can I find the part number for a replacement mat?
    A. Go on to www.realoem.com and enter your vehicle details, navigate to 'Audio, Navigation, Electronic Systems => Electric parts, airbag'.

    Q. How much will it cost to have the mat replaced?
    A. Prices range from £150 parts and labour upwards. This is a common fault on the E46 model series, dealers and specialists will be aware of the problem and most dealers carry a new mat in stock.

    Q. Can I buy the mat and replace it myself?
    A. Yes, be warned though it is a fiddly job. There is a good guide floating about on the net in a .pdf file. Go to google and type in 'e46 occupancy sensor replacement' and you should find it.

    Q. Can I make my own bypass sensor?
    A. Yes, see the attachment for the circuit schematic.

    There are several official BMW technical bulletins regarding the airbag system which aren’t available on TIS which I would be interested to read if anyone can get hold of them, they are;
    72 01 93 (2137) - "The [airbag] Watchdog subsystem has the ability to disable the Output Stage in the event of certain faults."
    72 01 85 (2042) - "If the SRS indicator light [lights up] the system is faulty; there is a risk of the system not operating in the event of an accident.
    72.01.85 Details of the SRS system
    71.01.93 Discusses the later-model Central Activation Module
    61.02.00 Describes the procedures for installing various SRS sensor wire harness repair kits.

    If anyone has any corrections or additions to the above then feel free to PM me and I'll update this post.

    Cheers

    Andy

    Hope it helps. Jim
    The older I get the wrong bit gets stiff !!
     
     

  8. The Following 2 Users Say Thank You to jcjdavis1 For This Useful Post:

    Matthew6009 (23-12-2015),Spaffy (13-08-2010)

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