check abs sensors

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C200 -98 classic AUT 280000km

I have a problem with my abs/asr lights being constantly on and the systems not working. Both lights are on immediate after start and always stay on. The lights used to go out before, randomly, but now they are always on.

I have checked fuses, changed the break pedal switch and cleaned both front sensors. Did not find any sensors at the rear wheels so I suppose there is one sensor on the axle for both.

the rpm and km/h meters work fine = the sensor on the rear wheels is ok?

1. the cruize control does not work
2. the kickdown does not work (yes im sure this is the reason, it worked fine whenever the lights would go off.. it shifts down when i press the pedal, but when it reaches high rpm it doesn't shift up)
3. and now after me "cleaning" the sensors (using wd-40 electric cleaning compound) the doors don't automatically lock above 10km/h (they did prior cleaning, even though the cruize, kickdown didn't)

does these symptoms point to a abs sensor? do they point to a specifik, ie the front left?

also read that you can check with a multimeter if the sensor is working correctly by reading the resistance. But where would you connect the multimeter since it is a enclosed system as far as I can see? Included two pictures.

http://public.openmindedprojects.com/ABSSensor_Givare.jpg
http://public.openmindedprojects.com/ABSSensor_Kontakt.jpg
 
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Thanks guys for the quick answer. television: thank you, long time reader first time poster!

did a quick search and it seems that people who get stuck in "limp home mode" 1-2 gear should change the ovp relay. But I don't have that problem, she accelerates nicely, changing gears without problem smooth and nice. Only have problems if I engage the kickdown, it then shifts down and accelerates, but wont change up gear unless I ease on the pedal a bit, hence stop pressing on the kickdown.

Should I still change the ovp relay or was it only related to the limp home gear problems?
 

teddycatkin

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I think its the source of most of you problems-or some other similar breakdown in the electrical system.
 

television

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When the OVP relay goes down the ABS will be the first to show up,,what the rest of the car does is dependent on the year and engine control systems in that car,.

Check the fuse on top of the relay if you have one
 
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How do you know if a model has this OVP relay? Is it based on time of production (facelifted classic 19980618) or has it something to do with equipment?

found this picture below, so I guess this is what I need to look for?
http://img229.imageshack.us/img229/3447/2015403745aq5.jpg

Is it easy to spot in the engine compartment or is it below a cover or such? Did a quick check this morning, but couldn't seem to locate it. According to the hayenes manual on models 98-> it should be located on the left side. So I unscrewed the cover (passanger side, up in the corner) and saw some wires, relays, fuses and a connection to the ecu I assume.. but nothing looking like that OVP with a fuse on top..)
 

bigasotonuk

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On your age C class you don,t have a OVP relay.
Regarding the ABS sensors, you could try measuring the resistance across each one and if one reading is off it might indicate the faulty sensor, but I would be inclined to get the fault codes read as this should eliminate any doubt.
To gain access to the rear sensor if it is the same as my 97 c class, remove the plastic cover immediatly behind the rear seats in the boot space, and the cable should be plugged in under there so a meter can easily be used on it.
 

television

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There is more to this,,if the ESP lamp is on, then the brake light switch can do this from 03-97.

To check the ESP on pin 45 of controller red and pink also pin 47 and the same colours for 12 volt, then check fuse f23/1f8 for a good fit

At this stage I would change the stop lamp switch its only £10 and can give 90% of your faults
 
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Damn was hoping it was the OVP relay or fuse since it seems it would be a quick fix. I have jump started the car twice and read that some fried the OVP while jump starting, I hoped mine problem was as easy.

television, I have already replaced the break pedal switch (located above the break pedal), if it is the same as the one you mention? Did this as a first step since it was so cheap to buy.

Thanks for the tip regarding the rear sensor. I guess that I will measure the resistance? Then I don't even need to spin the wheels? Have read that some measure the volts, while spinning the wheels?

Have searched but not sure what readings are correct, these sound good?
Front Axle Speed Sensors 850-2300 ohms
Rear Axle Speed Sensor 600-1600 ohms
 

television

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The other thing is a low battery voltage mentioned in my last post was under voltage, the standing starting voltage must be over 12 volts or these things cannot re set.

Do check the voltage on the ESP controller
 
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Ah ok I see.. will test that too but the battery is pretty fresh and fully charged prior install so I think its ok, but still will test it to be sure.

Anyway, I was in the garage today and tested the sensors with a ohm meter. The front right and back sensor both gave a resistance of 1020ohm, constant, but the front left gave no output, dead! So I took it off and exposed the cables close to the sensor body, tested cables and both gave a reading. So the sensor is definitely dead, and I will go and buy a replacement in the morning.

Holding my thumbs that this was the only problem and that it will be fixed tomorrow with the replacement! Will keep you posted ;)
 

television

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Sorry we cant be more helpful,,but these faults are the worst.

Full marks to you for getting stuck in:D:D
 
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No, no you are most helpful guys, I am very grateful!
 
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Changed to a new front left sensor today, but no luck :\
The ABS/ASR lights are still on, do you need to reset it in some way (turning wheel left-right), disconnecting battery?

The thing is, now the doors lock automatically when >10km/h after the sensor change.. Where do I go from here?
 

television

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There is only one paper on this that covers your faults and I can E mail it to you,,this is possibly a software update once you have fitted the new brake light switch.
 
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Read that models prior -98 only have one sensor on the rear but that models onward have two sensors, one on each wheel. I jacked up the car and discovered that mine sure enough has two sensors, they were hiding behind the heat shield on the wheel so I didn't see them the first time around.

Did a ohm reading, the left gave a reading of 1050ohms which was close to the readings of the front wheels but the right one was dead giving no reading at all. Cut the cord and tested it, had contact.. so it wasn't the cord but the sensor body. Will buy a new sensor tomorrow and fit it holding my thumbs.. ill keep you posted on the progress!

Btw, looking at the homepage of a local dealer there are three different sensors based on chassis number, but all of them are "no ASR". Does this mean that ill have to buy it from expensive MB?
 
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Success! I changed the right rear sensor today and started the car, the lights were on. I drove 20~ meters, still on. I drove a couple of meters more and did a hard break to stress the system, the lights went out and I felt the pedal pumping! Now the cruise control is working, the kick down is working perfectly, antispinn is working, pressing the ASR off button turns it off. Everything is working great again!

I want to thank everybody for helping me solve this!

Info below is for future reference when people are searching_____
keywords: abs, asr, sensor, kickdown, cruise control, break pedal switch, w202, ate

w202 C200 -98 280000km

Measured resistance on front sensors: ~1100 ohms
Measured resistance on rear sensors: ~1060 ohms

Model year 98 onward, two rear sensors behind the heatshield,
models prior 98 one rear sensor on the rear axle.

part numbers for my sensors
front left: a 202 540 23 17 (ate)
rear right: a 202 540 28 17 (ate)

I came to the conclusion that the door locking function when speed >10km/h is controlled by the front left sensor. Also my kick down function and cruise control did not function correctly/at all while I had a problem with the ABS system/sensors. This could be of some help to someone having problems with kick down/cruise and dirty/faulty sensors.

Again, thanks for the help guys - anybody having problems/help ask and I will do my best to help you.
 

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