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  #1  
Old 11-27-2005, 01:35 PM
Der Kompessar
 
Join Date: Nov 2005
Location: Michigan
Posts: 2
Shifter Console: Clean or Dry spilled liquids?

A coffee spill seems to have triggered electronic limp home mode (2nd gear only) in 99 C230. Working the gearshift while driving plus interior heat (it is below freezing here) seems to have rejuvanated the "D" light, which was not illuminating.

Wondering if there is anything to try today (Sunday) before taking to the dealer Monday. I am hoping the problem is one of mechanical contact rather than electrical damage. Earlier post suggests even if the shifter has returned to normal the car will remain in limp-home mode until the fault is reset.

Is is feasible to get at this mechanism to see that it is cleaned out?

I have pulled the cover up which houses the window switches and the "W/S" switch. Is it possible liquids in the W/S switch caused the fault? If so, any home investigation possible? Thanks!

(....Electrical limp-home mode ...In order to prevent damage to the automatic transmission in the event of an electrical fault, the gear currently engaged is held and the assigned diagnostic trouble code (DTC) is stored.
...MOST likely! some liquid has been spilled on the gear shifter! IT is a computer & computers don't like liquids!...
...the vehicle can only be driven in 2nd or reverse gear.
...The engagement of "N -> D" and "N -> R" will be very harsh, since the electronic control of the automatic transmission has been turned off.
This type of limp-home mode can only reset by repairing the fault and erasing the DTCs with the Hand-Held Tester (HHT).
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  #2  
Old 11-27-2005, 01:58 PM
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Join Date: Jun 2001
Location: Omaha, NE
Posts: 962
Do a search -- this has been discussed some time this year (and as I recall, the news is not good).
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'93 400E
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  #3  
Old 11-27-2005, 03:39 PM
t walgamuth's Avatar
dieselarchitect
 
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 22,073
i dont have one that new

but i used to spray electrical cleaner on the window switches when we spilled stuff on them.

guess the germans dont drink things in their cars!

tom w
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Old 11-27-2005, 04:13 PM
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Join Date: Jul 2005
Location: Eastern Panhandle, WV
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I believe that is why MB resisted including drink holders. Can you believe it, they must think that you are actually supposed to concentrate on your driving, not eat breakfast/lunch/dinner/snacks while going down the autobahn at 150 MPH!
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  #5  
Old 11-27-2005, 05:10 PM
ace ace is offline
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Join Date: Nov 2005
Posts: 33
boblane,

I can only give you info that pertains to my '97 E420. There the W/S switch simply supplies 12 volts to pin 3 on the Transmission Control Module when it is in W and 0 volts when it is in S mode. If your car is similar, the only way that I could imagine how this switch could cause limp mode is if instead of the full 12 v you are getting too low a voltage , either because the contacts are dirty and have built up resistance, or, because there is some current leakage through the coffee left on the switch. If the switch is not working alltogether the car would just be in S mode instead or W or vice versa not cause limp mode.At any rate, it should be easy to measure the funtionality of this switch at the TCM connector.

The main gear selector switch is a little more complicated, it is essentially a 4 bit binary switch which means it can give 2x2x2x2=16 different responses. Examples: 0001 ; 0010 ; 0011 ; 0100 ; 0101 ; 0110 ; 0111 etc. Out of these possible 16, only 8 are used and needed ( 1,2,3,4,D,N,R,P) So MB skips every other response which means that any single failing contact in the switch can not yield a "wrong" but nonetheless "valid" response from the switch. The only way it can go from one valid to the next valid reading is by two of the 4 bits changing state ( going from 1 to 0 or vice versa) . One faulty contact ( regardless of whether it is stuck "open" or stuck "closed")in the switch will cause a single bit change which will cause an invalid reading. This off-course the TCM can detect and it will most likely trigger the limp mode.


Attached is the combination of voltages that are valid for my car, notice that instead of the 0 and 1 in my example, they use 0 and 10 volts.
No idea if yours is identical so beware.
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Shifter Console: Clean or Dry spilled liquids?-gearshiftsettings.gif  
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