[W126 Coupe] Universal dash symbols

[Mister McGoo]

Thanks for the replies.  
 
I actually had not imagined that the mystery triangle warning light and the doughnut switch were related.  She had commented that the light came on momentarily when she turns into her driveway... accelerating slightly to get through a slippery mud puddle at the entrance.  This would explain the momentary light.
 
The rocker switch on the console seems to have an upper and lower position... obviously both momentary contacts... I assume "on" and "off".  Is the ASR active always for normal driving and the rocker manually switched "on" only when starting from a standstill in poor traction conditions?   (I apology, I no longer have the car here so I'm speaking from memory.)
 
In other words, what is the correct use of the console switch?
 
This car is a '95 E320 Estate, which I gather is the last year of the W124.
 
Thanks again /!\
 
-Bellamy 
 
 


From: dakota at mac.comDate: Wed, 3 Oct 2007 18:34:02 -0700To: mbcoupes at mbcoupes.comSubject: Re: [W126 Coupe] Universal dash symbols

Mister Magoo asked:
Hello all, Here is a question that the whole world likely knows the answers to except me.  I was asked earlier today....  On a '95 E320 S/W there is a warning light above the odometer on the face of the speedo, amber with triangle and (!) exclamation.  On the rocker switch panel on the centre consol there is (I'm quoting the owner now) "what appears to be a doughnut standing on its edge with worms."  (Personally, I would say its an inner tube with chains.)  Function-wise, it appears to turn its own tiny light on and off. The lady doesn't have an owner's handbook and NEEDS one.   Is it obvious that Benz-wise, I'm hopelessly stuck back in the 123/124/126 1980's??? - Bellamy
Bellamy, here is probably more than you would ever want to know about the ASR system. At the risk of incurring KBF's rath, here goes...


MB seems a bit confused on its name, and it's probably a matter of symantics and translation from the original German. Job 42-0800 (w124) calls it Acceleration Skid Control, while the Owner's Manual calls it Acceleration Slip Control. Acceleration Slip Regulation fits the TLA. ASR stands for "Anti Schlupf Reglung" in German.


To understand the "snow chain switch", you need to understand ASR a bit. ASR is a control system that activates the brake on the spinning wheel and depending upon conditions, reduces engine power output until the slip stops. There are several stages in the ASR activation which occur in milliseconds and are transparent to the driver.

In the US, ASR was an option from '91-on, on non-4matic vehicles only. My 300CE has ASR, with the  /!\  in the speedometer, just like the 4matic. It's tied in with the ABS and has four wheel speed sensors and a connection to the acceleration control system. There are three different control ranges in the ASR control mode using both a drive moment control circuit and a brake moment control circuit. More info is also contained in Brake System job 42-0800.

The acceleration skid control (ASR) will engage at all vehicle speeds, if one or both drive wheels begin to lose traction and spin due to excessive acceleration. While engaged, the yellow function indicator /!\ in the speedo lights up.

With the ASR engaged, the brake is applied to the spinning drive wheel until it regains sufficient traction. If both drive wheels lose traction and spin, the brake is applied to both wheels and simultaneously, engine torque is limited.

As traction on the road surface increases, the allowable engine torque also increases again and the brake is no longer applied to the drive wheels.

As I mentioned, there is a brake moment control circuit and a drive moment control circuit. The three control ranges of the ASR are:

A. Control mode with one skidding drive wheel and at wheel speeds < 40 km/h. The allowable slip threshold is higher for the Drive moment control than the Brake moment control, so the brake is applied to the slipping wheel. If it still slips too much, the Drive control comes in and retards the electronic accelerator control.

B: Control mode when both drive wheels skid or at a speed < 40km/h. Drive control has priority and retards accelerator. If wheels still skid, brake control is added.

C. Control mode when cornering at speeds between 20 km/h and 120 km/h. Depending on lateral acceleration, Drive moment control comes in sooner than for mode "B".

The console mounted switch, the "snow chain" switch, when activated, increases the speed threshold of when each mode will start to engage. This "buffers" the ASR a bit and lets some slippage occur when first starting out from a stop. 

There is no traditional locking differential; the asymmetrical braking independently applied to the rear wheels provides this function, sort of. MB has a different system for an automated rear end differential, called ASD "Autosperrdifferential".


Interestingly, I find a 1990 MB brochure mentioned that MB developed all three of their electronically controlled traction systems (ASD, ASR and 4Matic) in the same year - 1986.

The ASR was available in the S-class only (not in R107, W201 nor W124) in the Oct 88 GB "Recomended Price List for Cars and Factory Fitted Extras". 

It cost ~1500 to 1700 in then-year British Pounds (including basic cost, tax and VAT).

Another brochure I have says that ASR was available in the V-8 models in 3rd quarter 1986.

ASR was available in Europe on the 1990 W124 six cylinder gas saloons, coupes and estates with automatic transmissions, but not the 4 cylinder gas, or 5 or 6 cylinder diesel cars. It was offered on both the 1991 W126 and 124 models in the US. I believe it was approximately a US$2000 option. It came standard on the all 500E and E500 W124 from 1992 thru 1994.

Regards,
Steve

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