Reset the Check Engine Light - PeachParts Mercedes-Benz Forum

aldedmon · #1 09-24-2002, 12:33 AM

Well I tried the method prescribed by some on this forum(pressing the LED light switch for 8 -11 secs) to reset the check engine light to no avail. Michael offered an alternative which absolutely worked....Disconnect the battery momentarily and then reconnect.
Voila'...no more check engine light

JimF · #2 09-24-2002, 01:08 AM

needed here.

To reset the 'DTC' causing the CE light to come on, you must first bring up the code.

This is done by turing the ignition on (all lights in IC lit) and by pressing the sw about 2-3 seconds. Then the LED will flash x times representing the DTC.

Now you press the sw for about 6 - 8 secs within 20 seconds of seeing the code. Next turn the ignition off for 10 seconds.

Now you must repeat this procedure for every DTC stored in the Diag Module's memory.

What you did would not have worked. The battery works on early Mercedes but not on later models. You do, however, loose the radio when you pull the battery. That's the only possible bad part.

Once you know how to do it correctly, the sw/LED combo is very easy. This is explained in Menu #2.

aldedmon · #3 09-24-2002, 09:30 AM

Yes Jim, I'm sure you are correct.
I visited your sight and did follow these instructions to the letter.
However on the 93 500E, they are not applicable. With the car off and the switch turn on to illuminate all the lights, I did depress the button for 2-3 secs. Nothing happened. I put the switch in position 2?(radio operates only no idiot lights), tried it again...nothing happened. Returned it to position 3 tried it again for 2-3 sec and subsequent times for 8-11 secs and nothing happened. Hey maybe I have a bad LED device. Only after disconnecting/reconnecting the battery did the light go out. Others may have better luck

JimF · #4 09-24-2002, 10:38 AM

I've found that instead pressing the sw for 2 -3 sec, a better 'time' is 3 - 5 secs. If you can't bring up the code, then it can't be reset.

If it happens again, try experimenting with that time. And let us know.

aldedmon · #5 09-24-2002, 10:48 AM

On my car, and again, I can't speak for the other 10K 500E/E500 that were produced, the switch is non functioning from a "Self Resetting" perspective. I have a BMW 530iT. For it I bought a self resetting tool. The instructions say to hold the button for "X" seconds to reset the oil and "X" seconds to reset the service light.
I always have to hold it long/more flashes than the instructions say. So believe me when I tell you, I played with it pretty good. It don't work

Arthur Dalton · #6 09-24-2002, 11:07 AM

If you disconnected the battery, there will be no codes , including the single "no fault" until so many drive cycles.

Same goes for the single 'No code" after erasing any stored codes..

Also, the switch has to be pressed firmly to make a connection..
I have found that a pencil eraser end pushes it in better than a finger...

If it still doesn't work, make the led tool and see what you get-- that will verify the circuity and point to a bad sw/led..

aldedmon · #7 09-24-2002, 11:38 AM

When I pushed, the LED light did in fact light up, it just didn't cycle. As long as I held in, it would light RED. When I released it, it went out. I held it longer, it shown RED. I released...went out. Although the Check engine light is now out(disconnected battery), I may try one more time, pressing down on the switch really firmly with a retracted ball point pen to make sure I get a really good contact.
How do you make the tool??

Arthur Dalton · #8 09-24-2002, 12:38 PM

If the led is coming on with pressing the sw. , that is not the problem as the sw/led are OK

I sent the tool pic to you via email..

JimF · #9 09-24-2002, 07:10 PM

procedure. And I've seen it on many cars including my own.

Today, while at my tech's shop, Pat had just reset the CE light on a '92 400E. It was the O2 sensor.

But what's strange is right after the CE light is reset (and no codes showing on the AST Retreiver), the LED/sw combo gives no codes at all. IE, not even a single flash.

This also occurs on my car after I reset the codes. So it will work in a day or so. So try the LED/sw combo in a day or so, you will get 'one' flash. Hopefully, just one!

Arthur Dalton · #10 09-24-2002, 08:39 PM

There is a footnote in one of my procedure sheets explaining that the "1 Flash - No code" feature will not appear until the Dignostic Module has checked each and every system/component to satisfaction before it will re-instate to a No Fault condition. [ one flash]

This takes several drive cycles to complete... from temps, to rpms to o2 readings ,shift points, etc, etc....

I have seen it take a week..

aldedmon · #11 10-02-2002, 05:32 PM

Its been a week and several drives but still the LED doesn't function as many are saying it should. Does any one else with a NON California original destination car, have a similiar issue with the LED not "Flashing"?