CentralLine

So what is your trick to opening the longitudinal (the one closer to the front of the car) accelerometer? (part #933 806 153 00) At $1300-1700 I am a little concerned about breaking it while opening it. My microscrewdriver barely fits in the corners, and am finding it difficult to lift over all 4 tabs at once.

What does StoBempfindlich mean anyway? (sticker on the accelerometer)

I hate to say it, but the absurd cost of these two accelerometers alone makes me think twice about keeping the car, especially if these really were only $250 a few years ago.

Thanks

Staffan

Not answering your question, just asking another, sorry about that.
Is this for the Tiptronic system ?

CentralLine

No, not tiptronic, but rather the PDAS traction control system. There are 2 on C4's and one on C2's.

Computamedic

I seem to remember that I used a craft knife to pop the top of the box. It was a while ago now.

Regards

Dave

bhensarl

I used a pocket knife to lever the top of the sucker off. It's only held on by two little plastic abs. I think you'd be hard pressed to do too much damage to it unless you're really rough with it. I'm not really sure what you can clean inside, but please do write up any procedure you follow and the results. I konw I've heard of people cleaning them with compressed air, but I don't know what they did. Good luck.
Brian

DaveK

I didn't have any problem at all opening mine. Just a couple of clips and it popped right off.

To be honest - the top is only really a dust cover anyway. I'm sure if you broke the tabs, you could use tape to re-assemble it.

bhensarl

Okay, here's a pic. Go get 'em! Just wedge your knife in there and pry. Try to forget that you're using a common handtool to apply pressure to a $1700 part. That's the tough part.
Brian

CentralLine

Part A:
Thanks for all the pictures and advice. I actually had no problem getting into the part that is described in the above replies... just pop off the top. It was actually the other accelerometer that I was having trouble getting open. I ended up using 4 micro-screwdrivers under the 4 tabs while I inched (mm'ed actually) the unit out... only managing to break one of the tabs in the process and scoring the crap out of everything else. Luckily nothing (appeared) to be nicked inside. And actually there didn't appear to be anything to clean. So unless someone has more to add, I would not bother opening the accelerometer closest to the front of the car.

Part B:
As far as cleaning the "back" accelerometer (or lateral as it is called) I used a micro-screwdriver to remove the big clumps of magnetized metal shavings that formed between the copper plate and the magnet at the end of the "arm" part of the sensor. Then I passed a sheet of paper between the magnet and the copper looking sensor plate to remove more clumps. Lastly I used compressed air from my compressor to blow out the rest of the metal. In order to get the air between the magnet and plate, I removed the two small screws that holds the circuit board to the plastic housing. I was then able to lift the entire internal unit up by about 3mms, which allowed me to get the air between the parts that were previously obscured by the plastic housing. Be very careful, however, when you torque up on the "internal unit" as you will be flexing the 3 soldered contacts which connect the "unit" to the harness contacts. Lift too far and they will break. After this procedure the sensor "arm" moved much more freely, and hopefully I will have eliminated my fault codes (haven't tested the car yet)

The picture below corresponds to Part A above. Reference the picture from the pervious thread to see the accelerometer described in part B.

bhensarl

Great write up! Hope it works for you. Let us know.
Brian

CentralLine

Well, cleaning the accelerometer was the trick. I now have PDAS and anti-lock again. I also engaged the central diff lock and drove up to 40 mph as suggested in Adrian's book, which might have helped as well.

Now to tackle the distributor drive belt. The fun awaits.

jenskleis

Hi CentralLine,

Somewhere there is a post of mine about my troubles with cleaning the accelerometers on my C4. It was an expensive adventure.

You should be able to prise off the lid with a knife or a thin screwdriver.

FYI, "StoBempfindlich" means "Shock Sensitive" in German... As I said: be careful!!!

Take care

wf758

Thanks for this thread! I think it solved my problems.

My story is here.

aeroman

I may have one for sale if you want. Won't charge you 1700 either.

targatime

After 2 years of trying to solve this issue...I am posting another tread to see if anyone has a alarm code related to cell tower proximity and the PDAS warning light.

I've been told to clean my accelerometers...which I have done 3 times. One related question....does anyone know if there is an effect on the part if the small metal arm that is in accelerometer is kinking in a couple spots (generally straight, but still kinked). Very clean however. It is the forward unit.

So far, I've replaced my wires, distributor caps, plugs, rotors...but still alarming. The only thing left is my alternator and coils. I've looked for bad wires and grounding issues...but havent found any. I'm no expert though.

History of the problem......My car alarms in the same couple locations consistantly. The locations dont seem to be dependent on the miles I've driven. I could have driven 5 miles or 25...but when I go past a certain location on the highway....alarm goes off.

The only thing that seems common is that when the car alarms, I can usually see a celular tower nearby. It also seems that if I'm on a frontage road that borders the highway which goes past the same tower....I dont get the alarm. Speeds are about 25 mph less.

I never seem to have any braking problems as a result of this alarm...

springer3

Replacing the ignition coils stopped my problems with alarms. Both coils ohmmed out within the specifications, and there was no external sign of arcing or contamination. I think there was an internal fault causing arcing, and that triggers the alarms.