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modo
26-11-2008, 23:13
How to diagnose the problem with your Airbag light

Hi, I have been suffering since 2006 when I bought my E46 318iSE as the airbag light was always ON and I could not work out how to fix this issue.
In 2007 I was told that the problem is with my seat occupancy sensor (using scanner tool) but I was also told that the problem could be the sensor itself or the pad in the passenger seat.
In the UK, BMW dealers charge 40pounds for the sensor and 75 pounds for the pad itself+ about 3 hours labour at 150 pounds per hour so I had to pay around 600 pounds ($1200) to fix this problem.

Now I want to show you how to find out the problem with the pad or sensor. you usually get only one error for the sensor and do not know whether the problem is with the pad or with the sensor.

Do this:
After scanning the ECU and getting passenger occupancy sensor error:
make a circuit like this, you will need:
2 resistors 100 ohm each (or 200 ohm) not less than 100 ohm.
1 diode (rectifier) 1N4001 or 1N4002 or 1N4003 or 1N4004 or 1N4005 or 1N4006 or 1N4007

connect this circuit to your sensor (disconnect the seat pad's cable and connect it to the sensor [the little black box]) and CLEAR the error with your scanner tool. if the airbag light comes back then the problem is with your sensor NOT the pad. If airbag light does not appear then you have to change the pad in the seat (what I had to do....) and it is a great deal of pain but it worths to see the car is fixed! I found this circuit from a website and as I am doing electrical engineering I could easily work out what it does!

WARNING: This should never make you tempted to connect this circuit to your sensor just to have your airbag light off. In this case your airbags MAY or MAY NOT operate, I am not sure to be honest, but I am pretty sure that the sensor is actually disabled as it can not measure the variable resistance. Just simply order a new pad and on a weekend remove the seat and fix it (it took about 2 hours for me). It feels very good when something is DONE and DUSTED!


Another way of checking the pad is to measure its resistance (you need to have an ohm-meter) :
A faulty pad has higher resistance (mine had 13Mega Ohm) but usually the pad's resistance should be between 9- 10M Ohm with no occupant and when someone seats on it, it should drop to under 100 Ohm. That is the way the sensor can sense whether someone is actually sitting or not.

Sursa:E46Fanatics.com (http://forum.e46fanatics.com/showthread.php?t=615101)