W126 ASR On/Off Switch - PeachParts Mercedes-Benz Forum

BenzEnthusiast · #1 04-05-2014, 06:25 PM

I have seen ASR defeat discussed before, but I think I might have figured out an easier way. I'd like to be able to turn off the ASR sometimes, but not permanently disable the feature.

I have read of a method of using the the brake light switch, which on ASR equipped cars is different than non-ASR cars. It has 4 pins instead of 2 pins. The 2 additional pins are to disengage the ASR for braking, apparently. I haven't confirmed all of this information, so I could be entirely mistaken.

However, if this is true, than you could bridge these 2 pins that tell the ASR to turn off for braking with a switch and the ASR would remain inactive until the switch was returned to the un-bridged position. In other words, an ASR defeat switch that won't disable the ABS.

I'd try it on my own car, but I have the engine out of it right now. I'm looking forward to some feedback on this.

BenzEnthusiast · #2 04-06-2014, 02:38 AM

I have confirmed part of my theory on this. I read in these PDFs that when the brake pedal is pressed it automatically disengages the ASR system and switches to using the ABS system. Also, there is a different brake light switch (4 pin instead of 2 pin) used on ASR, ASD, and 4MATIC equipped cars so that the car will disengage these systems and instead use ABS to control wheel slip. So, the extra 2 pins on the 4 pin switch are only there to tell the ASR to disengage.

Now, I need to find out if simply bridging the connection between the 2 additional pins will in fact disengage it or if I have to add voltage from somewhere else to trick it.

I think this will be a way simpler way to disable the ASR on W126 & W124 cars if it works. Any thoughts will be appreciated.

http://www.w124performance.com/docs/mb/other/ASD-ASR-4MATIC-ADS.pdf

http://www.w-124.info/w124/ASD-ASR-4MATIC.pdf

BenzEnthusiast · #3 04-07-2014, 01:56 PM

On page 27 of this PDF it states the function of the 4 pin brake light switch.

"Stop lamp switch signal:
When the brake is operated, a signal is
transmitted to the logic section. The solenoid
valves are switched into the original position
by the logic section via the respective output
stages. In other words, ASR control mode is
terminated immediately."

It does this to go back to regular ABS mode, so using this to trick the ASR into staying off should have no ill effect upon the ABS function. Further more, this way of shutting off the ASR might not trip the ASR dummy light. If you do want the light on to remind you that it's switch off, I'm sure there is a way that you could tap the switch into the actual dummy light itself.

If this works, then it will be simpler than wiring directly into the harness of the ASR computer since everything will be done right above the pedals hidden under the knee bolster.

Is anyone excited to at least try this? I will do it as soon as I get my 420SEL running with the new engine and report back with results.