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Discussion Starter #1
As all of you know, speedometers in our cars<br>
lie. Of course this is intended, but there<br>
is a method to make sure at which real speed<br>
car is moving. Now, some of you will have an<br>
comfort ACC (Thermotronic). One may ask: what<br>
the hell has ac to do with real car speed?<br>
A/C uses various signals, like exterior temp,<br>
in-car temp measured in many points, temp<br>
and revs of engine, and car speed - to make<br>
temperature corrections more accurate.<br>
<br>
To enter 'debug mode' of Thermotronic you<br>
need to press and HOLD for more than 5 seconds<br>
'REST' button. Display will start to show some<br>
odd digits. Those digits are grouped in<br>
99 fields (some of fields are unavailable for<br>
reading, so unit simply skips them when you<br>
scroll thru all fields) and each field contains<br>
one digit - for some measured value. Number of<br>
the field will be displayed for 1 sec, then<br>
value, then again field number then...you got <br>
the idea.<br>
To scroll thru those fields, press LEFT and RIGHT<br>
'AUTO' buttons, left is one up, right- one down.<br>
<br>
Back to the subject, try to enter field #22 and<br>
move your car. Easiest method is to set speed<br>
limiter at some speed, then accelerate car till<br>
it hits the limit, let the speed stabilize for<br>
few seconds and read value from A/C display.<br>
For example if measured speed is 135 km/h display<br>
will show something like '1 35'. This method<br>
assures accurate measurement. My quick tests<br>
showed following values<br>
100km/h on the tacho - real was 96<br>
120 ' -- 114<br>
200 ' -- 194<br>
220 ' -- 213<br>
<br>
Didn't have approporiate road in the neighboorhood<br>
to test higher speeds :)<br>
<br>
Tell me how your speedo does!<br>
Hope you'll find my researches useful, or at<br>
least funny.<br>
If someone is interested, i have a full list<br>
of values displayed in the debug mode.<br>
<br>
This information applies to other MB models<br>
with electronic AC as well (i think that<br>
most of post-95 cars with acc will do). I'm<br>
not sure about field numbering, though.<br>
 

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Discussion Starter #2
I used a GPS

Great minds think alike. :) <br> <br> My GPS is totally accurate (+/- 0.1 km/h), so I used that. When the speedo indicates 100, I am acually doing about 96. <br> <br> Michael<br>
 

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Very interesting - I would definetely be interested in the full list of debug values.<br> <br> Only one thing puzzles me: What makes you think that the speed information from your AC is accurate? <br> <br> It must take it from somewhere. In a car with GPS it might take it from there (and then it's supposed to be quite accurate if you maintain that speed for some time). Otherwise it will take it from the same source as the speedometer ... and would simply be wrong in a different way.
 

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Re: Re: Test your C for speed!

Of course i've had not the a/c speed display<br> calibrated nor compared it with some good<br> reference - like michael W did with GPS receiver.<br> Altough i think that those values are pretty<br> accurate due to two facts - 1) it is really<br> not that difficult to measure speed of the moving<br> car and 2) A/C uses these values to calculate<br> some sophisticated things like wind chill factor<br> so it has to be correct and perhaps 3) - difference in displayed values is typically 4-3%<br> which is generally very 'popular' value of<br> speedometer errors, introduced by many car mfrs.<br> <br> Ok now for values:<br> <br> 1 in-car temp<br> 2 temp outside<br> 3 heater core temp, left<br> 4 heater core temp, right<br> 5 evaporator core temp<br> 6 engine coolant temp<br> 7 refrigerant pressure (in bars)<br> 8 refrigerant temp<br> 9 not used<br> 10 blower control voltage in range .8 - 6V (max)<br> 11 air pollution sensor<br> 12 sun sensor<br> 20 control current of aux fan<br> 21 engine RPM (x 100)<br> 22 vehicle speed, km/h<br> 23 terminal 58d battery charge, percent<br> 24 battery voltage<br> 40 software status register<br> 41 hardware status register<br>
 

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Discussion Starter #6
Re: Re: Re: Test your C for speed!

Thanks for the data.<br> <br> Regarding the speed reading, if it's taken from the same source as the speedometer (wheel) it depends on several factors (and not only the accuracy of the speedometer display) therefore I don't think it's very trustworthy ...
 

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Re: Re: Re: Re: Test your C for speed!

After studying documentation i found that there<br> is only one source - wheel sensors. Altough<br> it has to be very accurate due to one reason - <br> signals from same source are used for ESP and<br> navigation. I'm pretty sure that there is nothing<br> wrong with measurement itself, there is just<br> intended error in the main speedo display.<br> Of course this assumes that car rides on standard<br> tires (however, in the COMAND there is a submenu<br> where you can define tire size for correct speed<br> and distance measurement).<br>
 

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Discussion Starter #8
Will this work in any C320?

Will this work in any C320, or do you need a special A/c system or comand installed?<br> <br> Michael<br>
 

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Re: Will this work in any C320?

It will work in ANY mercedes with any kind of<br> automatic climate control (with digital display)<br> manufactured after 05.1995 (i believe). This is<br> according to the technical bulletin.<br> There is no need to have COMAND to do such things.<br> I've tested that on my 01 C320 and 95 C280.
 

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Discussion Starter #10
Yes, it worked... super cool. But, question:

...what are the other values? Many of the other registers indicate something active. This is extremely cool - anyone who can tell me more register values, please do.<br> <br> I will impress people hugely by showing them this - will make a litle plastic card with the registers, once I know them all..<br> <br> Thanks Michal. Very cool.<br>
 

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Discussion Starter #11
Yep, 96 indicated = 96 real.

Same here. 96 on the heating panel is 96 on the GPS = 100 on the speedo.<br> <br> Michael<br>
 

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Discussion Starter #12
Yep, 96 indicated = 96 real.

Same here. 96 on the heating panel is 96 on the GPS = 100 on the speedo.<br> <br> Michael<br>
 

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Re: Yes, got it - thx! I meant, though: the other codes (40-99 etc).

Ouch - as i said, my dox covers only those up<br> to 40. But i'll post them ASAP when i get them.
 

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Discussion Starter #16
Re: Re: Test your C for speed!

Hi,<br> <br> A question for any of you guys who have connected an after parket GPS into a C320. My tech cannot find the speed sensor wire to connect to the GPS anyone have any ideas on how to locate one? One Alpine instruction manaual said it is the green or green/black wire in passenger side kick panel, but there was no green/black wire there & the green one does not do it.<br> <br> thanks.<br>
 

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Discussion Starter #17
Taking delivery of C200 kmpressor Avantagrde. Any Checks!

Hi everyone. My Dad is taking delivery of his first Brand new Mercedes c200 kmp Avant.Ripshift. My question to you all what must mydad check for any shortcomings in the car. Also when taking delivery of the new car is there any tips or stories that fellow merc owners can sure with me. I am so appreciative of this forum. So any help or tips to make this wonderful experience as it is would be highly appreciative. This is the car my dad is buying for retirement. He was tailor for 42 years so the car is the cherry on the top. Oh Yes We reside in South Africa we make the car here. Aint that amazing! Take care and any tips or suggestion would be highly appreciated.<br>
 

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Re: Taking delivery of C200 kmpressor Avantagrde. Any Checks!

Congrats<br>
Before I took delivery of my car the local Sales Rep. has a check list which she has to go through with the customer.<br>
<br>
She has to explain and demostrate each and every function esp. the safety features of your car before handing over.<br>
<br>
My new C200 Kompressor, RHD mfr in South Africa, understand from the agent all MB sold in Singapore comes from Germany except the C model.<br>
<br>
Within a month and btw 600-1000km my car stalled 3 times. <br>
<br>
The last time my car stalled at traffic junction and almost got hit by the car behind me and the side.<br>
<br>
Dont know if German made MBs are more reliable or just my bad luck.<br>
<br>
I dont meant to sound rude but am rather disappointed paying almost US$100k for a C200 here<br>
<br>
How much ic my model selling in your country?<br>
<br>
Good luck and hapi driving.<br>
 
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