I have solved my own PDAS/ABS light issue! After having the problem diagnosed as a faulty longitudinal sensor (part costs something like $500), I removed this component to visually inspect it. The pendulum was not moving at all because it was completely gummed up with iron filings and other gunk. After a thorough cleaning using a toothpick, magnet, and a nail that I magnetized by rubbing it on the magnet, I am proud to say that the problem is solved. After all, it only took me ten months or so . The sensors are a little tricky to access just because they are installed in such a small area, but if I can do it, I am sure pretty much everyone else can too. Now I am back to having ABS and traction control (not that I really missed that extra understeer or anything).

 

Matt,

Are those the sensors located on the driveshaft hump, under the dash? Any issues getting into the sensor to inspect and then clean?

Glad you got it taken care of, and thanks for the tips.

Tom

 

Well done Scrooge. Have been having similar problems myself. Will check these sensors out even though the OPC says they are OK. Are these the ones on the transmission tunnel forward of the gear lever?

 

Yes they are.
I also had ABS problems and mine were fixed by JZM - when they cleaned out the sensors. A number of other C4 owners have found this was causing them problems as well.

 

By the way - one interesting thing:

When I had this problem, I didn't get warning lights, just very poor ABS - and I know a couple of other people who also had similar problems without warning lights. Scrooge is the first person I know of who has had warning lights due to the stuck accelerometers.

 

Yes, these are the sensors in the driveshaft hump that may be easily accessed via the little door on the right side of the trans tunnel (look for the two screws). There are two sensors inside there and they are easily removed with a (very) short Phillips screwdriver. After that, the covers pop right off with the aid of a key or similar instrument and one should be able to see if the pendulum is able to move freely. I was really suprised to find so much debris in the longitudinal sensor, but none in the lateral sensor. This may not be the solution to everyone's problem as I was often told that electrical interference somewhere else within the car was likely the cause of the warning lights. Anyway, its worth a shot for people to try before shelling out on expensive diagnostics / parts / etc. Good luck!

 

Have just had this problem myself, and would like to try cleaning the sensors.
This happened the day after going down a muddy building site type road, so wondered if I could have picked up some debris from there.

Does anyone have a photo of where the sensors are located ??