I have done these adjustments on my 1988 190E last week and my 1989 560SEL a couple of years ago without the knowledge of a "diagnostics mode". Such a mode might be true on newer cars but I never had to deal with that on my old clunkers.
The 560 has passed emissions and has been the most reliable car ever at over 300K miles.
What is your car model and year (maybe I should read the first thread )

I'm pretty sure it pertains to California models '88 and up, and all others '91 and up. My '93 requires it and Steve Brotherton said so!

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Ok, I found the led and button thing by the battery, whats the proper name for it by the way? #2 is the push button and #4 is the led. When I discovered this diagnostic connector the led was on solid. What should I do form here?

Observation: When the car is at operating temp and I try to increase engine speed via throttle cable the engine wants to die. Assuming since mixture isn't properly set, it's either too rich or too lean to keep up?


Here are the measurements @ 80C

Battery: 13.84v

Green connector of O2 sensor wire: .495v

Pin 3 of X11 connector: 2.093v (non-fluctuating)

EHA:0mA (non-fluctuating, almost as if I wasn't getting a reading at all!)

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'89 300E - 153k miles - California car - Black/Palomino

if the car is not running those values will not fluctuate.

The car is running.

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'89 300E - 153k miles - California car - Black/Palomino

Congratulations! What did you do to get it to run?

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1987 W201 190D

Actually got it running on Saturday, but didn't want to start up reliably and it ran not so well. Today I got to to run generally smooth (not as near as it did before though) and fire up rather easily each time.

So, does anyone know what to do when the led light is solid red?

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'89 300E - 153k miles - California car - Black/Palomino

If you are not getting any current fluctuation at the EHA while the car is running then you may have not connected the Ammeter correctly or your car's computer is fubar

or bad harness

Will have some time tomorrow to look at the car in the morning, I'll try to take a reading at the EHA again.

The led was sold it the diagnostic connector when I pulled the little cover off, should I do anything special, or just go ahead and hold the button down for a couple of seconds to get the codes?

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'89 300E - 153k miles - California car - Black/Palomino

I was able to pull the codes just now and came out with:

#5 - Oxygen sensor (I unplugged it while the engine was running)

#9 - EHA (also unplugged while engine was running)

#10 Throttle position switch - closed throttle position switch fault (idle)

I am going to clear all codes and see if my CE light goes off, that would indicate that the components in question are ok, and the reason the CE light is on, is because of disconnecting while running, correct? The CE light wasn't on before...

Whats the deal with fault code #10?

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'89 300E - 153k miles - California car - Black/Palomino

Cleared the codes and nothing came back after 10 minutes of idling, I'm sure that isn't a true test but like I said, the CE light only came on because I unplugged stuff while running. Also, the led went completely off after all the codes were cleared.

How do you put the car in 'diagnostic mode' to get duty cycle at pins 3 & 2 of the X11 connector?

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'89 300E - 153k miles - California car - Black/Palomino

Got around to putting the car into 'diagnostic mode' and got an average of .99 +/- .003 at pin 3 of the X11 terminal. I don't know, but that seems extremely low, right?

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'89 300E - 153k miles - California car - Black/Palomino