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tech4benz, Mercedes Technician
Category: Mercedes
Satisfied Customers: 320
Experience:  Master Certified , Dealership Employed and Factory Trained
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2000 Mercedes C220: CDI..The BAS/ASR light is on..brake light switch

Customer Question

I have a 2000 Mercedes C220 CDI W202. The BAS/ASR light is on. It has done this before and the fault was the brake light switch. The NC contacts had gone open circuit which I fixed withna bit of matchstick and a pir of lpliers. I thought it had gone again so , I just replaced the BL switch again with a new one out of the packet so I know that isnt the problem. It has 38 pin (OBD?) socket. I have been on various forums and I believe it is probably an ABS wheel speed sensor which has gone down. The cruise control has stopped working (as it did last time the lights came on). How can I find out which speed sensor has gone down and indeed if it is that? is it possible to meter the pins on the 38 pin. If so which pins do I test to where? To earth? What should the readings be? Usually the answer I get is "you have to go to Mercedes to get them to pull the codes". I have no intention of doing that. I will take the warning bulbs out first.Thanks for your help.
Submitted: 8 years ago.
Category: Mercedes
Customer: replied 8 years ago.
Relist: No answer yet.
Customer: replied 8 years ago.

Thanks Tech, I am happy to accept your answer and have done. I am a UK law expert on here with over 200 accepts so know how frustrating it is when people take loads of info and never accept.


So far I have fixed a faulty engine fan control module (damp), repaired fusible links in glow plug control unit, replaced single blade wiper motor, repl;aced brake rotors and pads twice all round, and finally made new bronze filled brushes for the AC motor (I wasnt going to buy a new motor!). I think I am up to it


I have a query on your answer which I am sure you can help. If I disconnect the sensor at the plug, there will, be no AC voltage on the sensor wire, it will be on the main loom. Do you mean patch into each plug while it is connected to the car?




PS The tyres are all the same. A good thought though.

Expert:  tech4benz replied 8 years ago.

Hello again,

Sorry, sometimes it's tough for me to find time to get on at work....The wires you need to probe into are for each wheel speed sensor.....and you want to probe into the connector with it already unplugged and you are actually testing the sensor side, not the car's harness side of each one......with it unplugged, use a paper clip(or some other kind of pin tool to get proper connection into each pin with it unplugged) and then hook up the meter to these pins......then spin the wheel you are testing to induce/create this AC voltage(THE VOLTAGE DOES NOT COME FROM THE CAR HARNESS SIDE)....good luck....Bob

Customer: replied 8 years ago.

Aha, induced by magnetic flux from wheel sensor. Makes sense now. Thanks. Now why didnt I think of that!???

Expert:  tech4benz replied 8 years ago.

Great, well I'm glad that you fully understand the always helpswhen you fully comprehend how something works when you're working on something, ....good luck with the car....Bob