View Full Version : What Caused This Anti-Skid Regulation (ASR) Anomaly?

10-25-2013, 04:56 PM
I recently experienced an ASR anomaly I've never seen before. Maybe someone could provide the reason(s) which caused (or could cause) the anomaly.

ASR light would come on (energize) after about 1/8 to 1/4 mile of driving. If I start the car and just remain stationary, the light would not be energized. This condition existed for several days.

I washed the car, and flooded the calipers/brake pads/rotors with high pressure water. The condition still existed for several days post car wash.

Now, the past two days (100 miles post car wash), the ASR light no longer is energized after car has been in motion as described above.

Why? What would cause the ASR light to be energized - a temporary differential sensor malfunction? Brake pad sensors malfunction? About 10,000 miles ago, I had the Safety/Neutral Switch replaced on the transmission which solved an intermittent an ASR/Limp Home mode malfunction. Car has ~ 190K miles and well maintained.


10-25-2013, 09:09 PM
Exactly what happened two weekends ago with my wife's E320 wagon.

Remove your wheels and take the ABS/ASR sensors off, and check them for iron filings that are blocking the magnets. I recently had a similar deal (except I had ASR dash light (not the speedo triangle light)) and the car went into limp-home mode. The sensors were PACKED with iron filings. I also had a code at the same time for a neutral safety switch, so I changed it with a spare switch, and cleaned the sensors. No problems since.

Also, are your battery and charging system working well?

Brake pad sensors have nothing to do with it. The NSS are really poor quality these days -- they are being made in Eastern Europe and are not the same quality that they used to be. I have replaced THREE of them now on my wife's E320 wagon. The latest one I just did was made in Germany. I have a spare one that is about 10 years old for my E500 ... have never blown an NSS either on my E500 or my 560SEC...only on the E320 wagon. They're lasting about a year and a half. Factory MB parts too, not aftermarket. My mechanic here also tells me that he is going through a lot of them on customers' cars.

10-25-2013, 09:46 PM
"ASR light would come on (energize) after about 1/8 to 1/4 mile of driving. If I start the car and just remain stationary, the light would not be energized."

I have had exactly the same symptoms on my 93!

I have not checked the wheels and taken the ABS (http://www.500eboard.com/forums/showwiki.php?title=ABS)/ASR sensors off, to check for iron filings blocking the magnets.

That would be a great find if that is the problem.

10-26-2013, 01:35 AM
Driving home from getting my face-lifted car MoT'd after about 4 miles I stopped at some traffic lights. Pulling away I had juddering in the car. To keep with the traffic I powered on until I could stop; before I could find somewhere to stop the judder stopped. Puzzled I pull over and did a "fix limp home" engine restart. I drove home without problems and there has been no reoccurrence. I have not looked at possible causes yet.

12 April 2014, The ASR light was on virtually all the time so I had a look at the sensors. The Allen Socket Head Screws were tight with some thread locking compound to be seen. Both sensors looked the same with fine iron filings clinging to the sensor. I cleaned them with steel wool and then a WD40 spray and soft paper towel to clean before re-fitting. The sealing washers were both in good condition; which is quite remarkable after so many years of use. ASR light is now off.

10-27-2013, 09:30 AM
Can someone remove their wheels and check their wheel sensor magnets? It's a 10 minute job per side on the front. I'd be interested to see what folks find. I am going to do this on my E500 as well, and will take some photographs of the process.

10-27-2013, 06:34 PM
Screw ASR. Pitch those pesky sensors. Get you official AMG Superbird rear deck spoiler & make your tire treads stick to the pavement like glue!

10-27-2013, 06:58 PM
Screw ASR. Pitch those pesky sensors. Get you official AMG Superbird rear deck spoiler & make your tire treads stick to the pavement like glue!

I have to hang my head. :barf:

10-27-2013, 07:06 PM
At least I don't have to put in one of those "ASR defeat" switches if my ASR light keeps illuminating.
I guess my ASR IS defeated as long as the light is on.

10-27-2013, 09:04 PM
I guess my ASR IS defeated as long as the light is on.:e500launch:

10-28-2013, 08:46 PM

I'll give my wheels a breather this weekend and I'll photograph what I can. Thanks for the possible cause. Electric systems appears to be strong - replaced the battery not too long ago with one of those E55 gel-type batteries. No other system errors have been observed.


10-28-2013, 08:59 PM
Norm, be sure to pull your codes. On my wife's wagon, I got a NSS code (which was probably the cause of my issue) but I inspected and cleaned the sensors anyway, so they could do their job. I have seen that (blocked sensor) listed as a possible cause of LHM and ASR issues on other forums.

12-05-2013, 11:51 AM
My ASR pump runs for about 60 sec.; then cuts off and ASR light illuminates.

Still code 21 on pin 6.
"ASR pump charge".

12-05-2013, 12:32 PM
Sounds like your pump is defective.

Norm ... whatever happened with your situation?

03-01-2014, 02:01 PM
Update - work (paycheck job) has been my priority for the past two months so I've lived with the ASR light coming on after ~3 minutes of engine running and not moving (just idling).

The master cylinder brake fluid reservoir was substantially low on brake fluid when I came home one night - filled it up and brought the car to my Indy.

I took the car to a new Indy to diagnose and they pulled the codes and came up with code 21 on pin 6. "ASR pump charge". They said they inspected the Master Cylinder/ASR Pump area and calipers for wetness/leaks and everything appeared dry. Where did all the brake fluid go? In the ASR Pump Accumulator? My Indy flushed the system with ATE SL.6 and bleed the brakes. I'm going to watch the reservoir level very closely, but it still doesn't answer the question - where did the brake fluid go?

I would appreciate if any of our members have any MB ASR or Brake System documentation or insight, could you post it to this thread or provide a link to the information? After doing research on this site, it appears many of us are experiencing similar issues with the ASR system.

Thanks in advance.


03-01-2014, 03:24 PM
Two more places to check for leaking fluid when you can't find any leak at the calipers, hoses, hard lines, MC, or ABS/ASR assembly:

1) The ASR accumulator, inside the driver fender liner

2) Inside the power brake booster

A failed master cylinder seal can allow fluid to leak into the booster. I've not had this happen on a 500E but I've seen it on other MB's. The booster was half full of fluid! Replacing the MC cured that instance.


03-01-2014, 09:06 PM
Thanks Dave ... I'll proceed with your recommendations. Stay tuned.