I purchased a '95 E320 with 81,xxx miles on it. It ran and runs great. Problem is the check engine light came on recently while in Hilton Head, SC. I stopped by at the dealer in HH and asked could they scan the code. The lady told me to just check the gas cap to insure that it was tight which it was. I had put a can of Outlaw fuel injection cleaner in it (I have done this to all of my cars at around 80k miles) and when the tank got down to around 1/4 tank I filled it up again with Amoco 93 octane then drove it for 30 miles. The light did not come on while driving. It came on when I started up the next day. I unhooked the battery for 10 seconds and the check engine light went off and then came back on after about 25 miles of driving. Do I need to replace the O2 sensor? Where is it located - do I get to it underneath the car or under the hood? Is there another place to reset the check engine light? Otherwise it runs great and I got 25.9 mpg on this last tank of gas. Any thoughts/ideas.
Thanks,
engatwork

As you have found the check engine lamp is to monitor EMISSION related problems only! Have a trusted (trained) technician with scan tool retrieve codes from computer. The dealer at HH was incorrect!! 1995 cars do not have any monitor for gas cap being removed w/driving. Most all cars starting w/1997 do have monitor (V-8 & V12 cars in 1996). Don't spend $$$ until computer is tested.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V

thanks for the reply MB Doc.
Will it be ok to drive it till I can get it checked out? I am under the assumption that since it is running so good then it should be ok till I can get it in.
Opinion??
thanks
engatwork

Just remembered something else I did prior to the light coming on. I "topped out" the fuel filler neck on that fill up prior to the light coming on the next day (this has been a bad habit of mine). Would this have had anything to do with it?
Thanks,
engatwork

This car does not monitor fuel tank at all. You have a problem in the emission control system. Drive it and get it checked. Dont do this yourself, you will waste money.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Again check engine means emission related problem!! Too much fuel in tank isn't a problem except the emissions (from fuel vapor) when filling to the air around you. If the fuel mixture is too rich & you continue to drive then damage can happen to catylst, other than that only the red light is a bother. Have it scanned & then make repair.

MB Doc - wouldn't the gas mileage suffer if it was the O2 sensor?
I fully intend to take it in as soon as I can get an appointment. You do not know anyone that can scan one on a weekend do you? I would be willing to drive to Atl. to get it done.
I was out detailing it this morning and found the sensor in the cross over pipe from the air cleaner box was extremely dirty. Cleaned it up and will see if this makes any difference over the next day or two. My gut feeling is that I screwed up the O2 sensor by running the fuel injector cleaner through it.
thanks,
engatwork

Fixed the problem. Cleaning that sensor that is in the cross over pipe from the air cleaner box over to the intake manifold area seems to have resolved the problem. I would assume that it is an inlet air temp sensor (would like confirmation please). Anyway, I cleaned the "gunk" build up off of it and reset the check engine light and it has not come back on after hours of driving.
engatwork

The 94-95 E320 (124 body) has on-board diagnostics to monitor the emissions system. If the light has come on a code has been set and it DOESN'T need a scanner to be retrieved. Even if the light is now out the evidence of that code will remain for something like 40 or 80 drive cycles.

The code can be retrieved on these two years of 124 chassis (and some Ca models of other chassis) without scan tools. The impulse light is built into the diagnostic connector. There is a button next to the red led. Turn key on, engine off, and push the button and hold for 2-3 seconds. Release and the led will blink a code. One blink is "no faults". If a code is read, do the process again to read a second code. Keep reading codes till the first code re-appears.
The diagnostic connector is in the well in front of the battery, mounted high on the bulkhead separating the area from the motor. It has a two width rectangular cover with a small straight ridge for gripping and removal. Underneath are 16 round ports and the button and led. The cover may be missing.
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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[This message has been edited by stevebfl (edited 06-25-2000).]

Many times we can read a code & if we have enough information we can make a partial diagnosis. With a GOOD scan tool a good technician can look at all of the engine control modules (3 on this model) & make a better long term diagnosis of exsisting problems. When you look at the module that turn on check engine light it only provides a numerical code that must be translated into real world diagnosis. Looking into fuel system & idle speed (electronic accel) will give a much better idea of problems. The IAT sensor that you have cleaned should be replaced as they go open circuit at times & will trip check engine again.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V

Ok guys - I went out and ran the test with the led. I pushed the button and within a second or so the red light came on and stayed on until I released the button. Within a second or two it started flashing - 12 short flashes spaced evenly apart. I repeated the procedure and got the same results. If anyone on here can tell me what the 12 short flashes indicate I would appreciate it. In addition, does the instruction manual on CD that is for sale in the Parts Shop tell what all the various combination of flashes mean? I used to have a Mazda MPV van that indicated what the check engine light coming on meant by the same means but when you activated it it would actually flash the check engine light. I think code indicators that work like this are pretty neat.
thanks in advance ya'll.
engatwork

I don't think the CDs will have this kind of info. This info is provided in the diagnostic manual which isn't on the CD. Sorry I don't have the info at home.

steveblf or anyone else that may have access to the diagnostic manual could get an opportunity and see what the 12 short flashes mean and post it on here I would appreciate it very much. Is the diagnostic manual for this vehicle available for sale anywhere that any of you know of?
thanks
engatwork

I called the service advisor at the dealer today and he told me that they have no way of telling what the 12 flashes mean because they just hook a computer to the car and read the code. In addition, after I explained to him all of the prior post information (I left out the part about the fuel injection cleaner though) and told him that the car is running good and getting good gas mileage he said that he would not worry about it. He said that if it was the O2 sensor that had gone bad then it would not be running very good.

I will just let them check it out when I take it in for the 90k service.

I am still curious what the 12 flashes mean and would appreciate anyone on here looking and letting me know if they have access to the diagnostic manual.

thanks
engatwork

I emailed you a list of codes. It is an attachment. Hope you get it let me know if not.

On it you will find that the code twelve is a easily verifiable code as it indicates an open or short in the O2 sensor heater circuit. These are the two white wires on three wire sensors. It is a heater coil around the sensor to heat it. Lack of this heat causes the sensor to stay in open loop too long or maybe always.

Check with ohm meter across both wires. I don't know the ohm value but it takes about 1amp. E=IR says about 12 ohms. Check each of the wires to ground. You should have open circuit to the hundreds of thousands of ohms.

You can only get the heater with the sensor though.


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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician