I have a 1992 400E with 184K Miles on it. The car runs well and starts easily. I need a California Smog Check and have to use a Test Only Station.
The Check Engine Light (CEL) is On Continously (has been for quite a while) and the Smog Check shop says the Check Engine Light (CEL) On will definitely cause the car to fail the Smog Check.

1: How to reset the Check Engine Light (CEL) on the 1992 400E? I was told that disconnecting the battery for a minute or so will reset the light, but no success thus far.

2. Will the Check Engine Light ON cause the car to fail California Smog? This car is always near the limits on the Smog Test. Warming it up thoroughly with some high-speed driving etc. really helps.

3: Does the 1992 400E have the Push Button and LED for getting a trouble code output? How does it work? I have read lots of posts and it is unclear to me how it is setup on the 1992 400E.

Thanks,
Kim

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1992 400E (W124) - 177K Miles - fun car!!

Big question is how to Reset the Check Engine Light (CEL)?

1: How to reset the Check Engine Light (CEL) on the 1992 400E? I was told that disconnecting the battery for a minute or so will reset the light, but no success thus far.

If disconnecting the battery on the 1992 400E will not work, what is the correct procedure?

Thanks for the help.

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1992 400E (W124) - 177K Miles - fun car!!

Yes, a check engine light will cause your car to fail CA Smog Test. The protocol includes both emission control electronics and exhaust gas emissions. California and some other states are moving toward electronics only testing and dropping the emission portion of the test.

Since the light is on for a reason, you need to determine the problem. Even if you could clear it, it would likely reappear before you got to the Test station.

Check the archives for posts on how to determine OBD codes for your model/year.

Good luck.

Can you help me with how to reset the Check Engine Light (CEL)?
I realize that I need to get the codes also, but I want to clear it and see how long it takes to come back.
Thanks,
Kim

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1992 400E (W124) - 177K Miles - fun car!!

There is a push button LED, probably with a plastic cover on it next to where it says "battery in trunk." The LED only tests the diagnositc module because that's related to emission problems. Once you have found the push button, turn the ignition on without starting the car. Then hold the button down for three seconds. Whatever fault you have will be represented by the number of flashes. It will only give you one code at a time, so if you have more than one code, you will have to repeat the process.

The way you clear these codes is to hold the button down for three seconds, let it flash whatever fault code (I would also write it down), then hold the button down again for 10 seconds. Then, immediately turn the ignition off for 15 seconds.

For every code on your diagnostic module you will have to repeat the process.

There is a code that is common with these cars and that is code 19. Check out the article in this link (scroll down). You cannot reset this code. http://www.k6jrf.com/MB_S500.html

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

Yes and after you clear it, go directly to the smog place before it comes back. I had to do this when I bought my 400e. Previous owner had put cheap gas in it. Cleared it and 9 months later, still no CEL

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2000 SL500 - daily driver
1993 400E - project
1981 300D - sold
1982 300TD - sold
1979 450SL - sold
1977 450SL - sold

Ok hop on over to benzworld dot org and look upp how to make a code reader as the 400E and 500E dont have a built in reader. Use it to check codes, reset the computer, run the car for 30 min varing speed and see if CEL comes on. If it does get codes and repair.

Dont try and cheat, if you remove the light and it doesnt come on it will fail smog for no CEL. I have lived in CA and they are nuts about the CEL. My 93 400E doesnt even have a CEL as it was a dealer option. Its just a set of wires run to the computer to light when codes are stored.

You may be right about the LED tester, macdrone. I was thinking that if it had a check engine light--and I know some do not--it would also have an LED tester, up until the end of 1994, when they were discontinued. My old 93 400E and existing 1994 E420 have a CEL and LED tester. In any case, I agree that building the tester should be done to pull any of the codes on modules other than the DM.

For whatever reason, in Arizona, the state emissions inspection authority did not require me to show them an operable CEL (verify that the CEL has not been disconnected) when they tested my 1993 400E or my 1994 E420.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

If they dont just pull the bulb. The computer will hold helpfull codes if you dont pass emission though.