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  #1  
Old 11-16-2009, 04:13 PM
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'89 300 SE - CEL

My check engine light on my '89 300 SE came on two days ago. I disconnected the battery, with made it go out, but it came back on within about 15 minutes. The car starts, runs and idles perfectly. I can't detect any fault. I checked the duty cycle and it's right at 50%.

I spent many weeks tracking down a start,stall,start,stall,start,chug-chug,run fault, during which I replaced many parts, the last was the injectors, which cured the problem.

Where do I start to find out why the CEL is on, when the car is running perfectly? Any hint as to where to start would be greatly appreciated.

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Old 11-16-2009, 06:53 PM
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You probably need to pull the code from the diagnostic connector.
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Old 11-17-2009, 08:07 AM
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Depends on the computer version.

California versions have a red LED & pushbutton on the diagnostic connector.

Federal versions do not have that diagnostic ability.
On federal versions fuel mixture & O2 sensor readings are the only way that the check engine lamp is triggered. IF the mixture is too rich OR lean the O2 sensor won't function & after 5 minutes of no sweep the check engine lamp will come on.
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Old 11-17-2009, 09:55 PM
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Code reading 5 "flashes."

Quote:
Originally Posted by M.B.DOC View Post
Depends on the computer version.

California versions have a red LED & pushbutton on the diagnostic connector.

Federal versions do not have that diagnostic ability.
On federal versions fuel mixture & O2 sensor readings are the only way that the check engine lamp is triggered. IF the mixture is too rich OR lean the O2 sensor won't function & after 5 minutes of no sweep the check engine lamp will come on.
It's a California version, with the red LED & pushbutton.

I turned the engine off, then turned the key back to the "run" position. The red LED was on. I had to hold the button down for a long time, but the light finally went out, and then flashed 5 times. I looked the reading up and it says, "Exhaust gas recirculation faulty." I didn't think the 89 300SE had EGR and I don't see one mounted to the exhaust manifold.

Does this make any sense? I installed a new O2 sensor in August, about 6,000 miles ago. Could this have gone bad and caused the reading I see?
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Old 11-17-2009, 11:24 PM
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5 Flashes indicates the O2 sensor on your model 126.024



I would make sure its all hooked up ok before removing it. Make sure the connector is getting voltage.
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Old 11-19-2009, 09:56 AM
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Aha! The code fault table I used was the one Authur Dalton had posted, and I wondered if perhaps it was for different models, but couldn't find anything else. This is a big help.

A failed O2 sensor makes sense. I had just put nearly $2,000 into the car, and got "penny wise and pound foolish" on the O2 sensor I put in. I found it on ebay for a low price and got what I paid for. I now have a new original on the way.

Thanks for pointing me in the right direction.
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Old 11-30-2009, 10:54 AM
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A new Bosch O2 sensor fixed the problem.

I replaced the no-name universal O2 sensor with a Bosch that has the correct electrical fitting to plug into the car's wiring harness and it solved my problem. I cleared the code and the CEL light has stayed off for over 1,000 miles. Better still, I made two 600 mile trips since then and the milage is up a bit, 23.5 mpg vrs. a former best reading of 22.3 mpg. Plus I made the exact same trip the week before, with the defective O2 sensor in place and got 19.4.

The no-name universal came from an eBay seller in a box that was not marked as to the country of origin, but I suspect it was China. It's a good supplier & brand to avoid - carpartswholesale

carpa
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Old 01-08-2011, 03:27 AM
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Smile cel

I think this is whats wrong with my 90 300se how did you clear the code/light?
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  #9  
Old 01-08-2011, 05:35 AM
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Hey, guys I posted a sticky (well, MB Doc posted it for me) at the top of the Tech Help thats gives the CEL error codes for Mercedes models 1988-2000. Its a pdf with pretty much every code regarding every mechanism that can trigger a fault code, please check it out.

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