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1994 Pearl Black SL600
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48 Posts
Discussion Starter #1
So I came across this neat post over on the PeachParts forum about how you can read and erase diagnostic codes thru the climate control temp display. I was ready to call BS on it until I went out and tried it with my 94 sl600 and it works! The only problem is I don't know how to read the information that I am being given. I erased any codes I had (I have been getting a CEL on and off for the last few weeks) to get a fresh start since I have recently done some repairs/upgrades etc. Anyway, I have pulled codes via the LED method in the past but this new way is SOOOO much easier - IF I can figure out what the info I am getting means. Here is the procedure that worked for me:

Retrieving Stored Diagnostic Codes
1. Turn temperature selector wheel into the white area.
2. Ignition to Position 2 with engine off or on.
3. Within the next 10 seconds, press the "F", "RECIRCULATE AIR" and "REST" buttons simultaneously for 2 to 4 seconds.
4. The display will show the permanent DTC's stored. Press the "RECIRCULATE AIR" button after each is displayed until the display reads "END".
5. Press "RECIRCULATE AIR" button again and the intermittent DTC's will be shown. A square is shown after each of these DTC's to indicate it is intermittent. Press the "RECIRCULATE AIR" button again to see the next intermittent DTC and continue until "END" is shown.
6. To erase the DTC's: switch ignition from off to Position 2 and within 10 seconds press "RECIRCULATE AIR", "REST" and "UP" buttons simultaneously until "---" is displayed.

Some examples of what I am seeing displayed are:

"73" flashes and then a number...and then "73" followed by another number...and then "73" and another number so I am guessing "73" is a category and the subsequent numbers indicate various codes (when I say "another number" comes up I mean it is displayed after I have pushed the RECIRCULATE AIR button as instructed above for moving on to the next code)

"15 degrees C" (degrees is displayed as the symbol - not the word) and then that is followed by various numbers after pushing the button for the next code just like with "73" above. I also see "24 degrees C", "23 degrees C", "29 degrees C" with numbers after each.

"10U", "37U", "38U" and "42U" each also followed by various numbers like described above.

What I am looking for is what "73" or "10U" or "15 degrees C" mean as well as the numbers that I see following. I am not sure if they match up to those found in the trouble codes resource that I have used for the LED method of code pulling since some of the numbers displayed were over 30.

Anyone have any knowledge they would like to share?
 

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1994 Pearl Black SL600
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48 Posts
Discussion Starter #3
Hmmm...so why was it then that when I erased the codes using the procedure I listed my CEL was gone? AFAIK the CEL is related to emissions or fuel delivery and not much else. If those diagnostics are for is heater stuff why would it clear the CEL?

BTW I didn't post the whole procedure as it was listed on PeachParts - here is the whole thing (and there is a seperate procedure it seems for climate control codes and then diagnostic codes):

Reading Actual Values
1. Ignition to Position 2 with engine off or on.
2. Press the REST button and within 1 second press blower speed button 4.
3. The temperature window will alternately display the test step number (ex. "02 = in-car temp.) and the actual value.
4. Use the "F" and "C" keys to navigate to the different tests.

Test 02 = In-Car Temperature Sensor
Test 04 = Outside Temperature Sensor
Test 06 = Evaporator Temperatrue Sensor
Test 08 = Heater Core Temperature Sensor
Test 12 = Engine Coolant Temperature Sensor
Test 14 = Temperature Selector Wheel Setting
Test 18 = Vehicle Speed Signal (km/h)
Test 20 = Soft Top OPEN ("u") or CLOSED ("o")
Test 22 = Power Supply Voltage
Test 83 = Not Used
Test 84 = Blower Motor Voltage

To exit this test mode press "0".

Retrieving Stored Diagnostic Codes
1. Turn temperature selector wheel into the white area.
2. Ignition to Position 2 with engine off or on.
3. Within the next 10 seconds, press the "F", "RECIRCULATE AIR" and "REST" buttons simultaneously for 2 to 4 seconds.
4. The display will show the permanent DTC's stored. Press the "RECIRCULATE AIR" button after each is displayed until the display reads "END".
5. Press "RECIRCULATE AIR" button again and the intermittent DTC's will be shown. A square is shown after each of these DTC's to indicate it is intermittent. Press the "RECIRCULATE AIR" button again to see the next intermittent DTC and continue until "END" is shown.
6. To erase the DTC's: switch ignition from off to Position 2 and within 10 seconds press "RECIRCULATE AIR", "REST" and "UP" buttons simultaneously until "---" is displayed.
 

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Y2K SL500 Silver
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8,660 Posts
Hmmm...so why was it then that when I erased the codes using the procedure I listed my CEL was gone? If those diagnostics are for is heater stuff why would it clear the CEL?
The Climate Control Diagnostics did NOT erase your CEL. You may have cleared them some other way.
 

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1993 600SL, 1973 450 SL,1998 SLK 230,2018 C300, 2019 Ram 1500 Laramie, 1968 Firebird,
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5,303 Posts
If a sensor condition repeats beyond a preset number of fault cycles it trips the CEL. If the fault is absent for a certain number of ignition recycles, the CEL will reset. It can also be erased using the diagnostics or the built in code reader on the 93,94 models.
 
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