On my 94 SL600, I get ASR light on sometimes,
This is how it goes in every couple of days, I start the car in the morning and hear ABS/ASR pump run for like 10 15 seconds, then shuts off. within couple of minutes it starts and shuts off again, this happens usually 3 to 4 time, and then ASR light comes on and pump doesnt start anymore. Each and everytime after this incident I get code 22 "Pressure switch leakage" from socket 6 (ABS/ASR control module).

I have replaced the brake fluid, and checked all the hydraulic lines and didnt find any leaks whatsoever. After replaceing the brake fluid it did help a little bit but not too much. I followed alldatadiy instructions and tested the Wiring that goes between the control module and ABS/ASR pump, everthing is in accordance with specified values. I have tested the Hydraulic system and pressure values are also satisfying. Last option is replacing the ABS/ASR pump to see if it makes a difference.

On the other hand, I felt that while this incident is happening, I feel the brake pedal gets slightly firmer like Brake booster is filled with air. Or when you turn the engine off brake pedal gets firmer, its almost like that, its not that firm but I can feel a little firmness. Also, while this incident is in progress it usually lasts 1 to 5 minutes, Engine idle is erratic, like there is a vacuum leak or something like that.

My theory is, I am guessing there is a valve or something which controls the vacuum system. when it malfunctions it causes an erratic idle and causes the brake booster fill with air. and when I apply brake pedal, system recognizes that there is not enough pressure and turns the ABS/ASR pump on to pressurize the system. However, after cycling couple of times system is still not pressurized enough, then the control module thinks there is a hydraulic leak somewhere and turns on ASR MIL light and turns off ABS/ASR pump.

Does this make any sense! does this theory at least sound logical?