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Old 09-26-2001, 11:32 AM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
Check engine light -- 300E

Was driving along the other day when I smelled burnt plastic in the cabin. Looked under the car and found that a plastic bag has stuck to the cat converter and got fried; it eventually burned itself away.

Well, a day later the check engine light comes on when I'm at a stop, but disappears when I hit highway speed.

Any clues what's going on here?

Thanks for any replies!


'91 300E, 199k
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Old 09-26-2001, 11:42 AM
Michael's Avatar
Join Date: Jul 1999
Location: CT, USA
Posts: 2,699
O2 sensor is the only device that'll set off the "check engine" light. You can try running some Techron or other fuel system cleaner through, but likely you need to pop for a new O2 sensor.

Good luck!
"If everything seems under control, you're simply not going fast enough" --Mario Andretti

1995 E500 street car
1986 Porsche 944 Turbo S track car
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Old 09-26-2001, 01:17 PM
Registered User
Join Date: Aug 2001
Location: secret
Posts: 3,044
My local ******** tech told me that there are only three things that will light up the check engine light: the OVP, the O2 sensor and the coolant temperature sensor for the fuel injection. I changed all three and mine is STILL on and I'm not that fond of the color RED!
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Old 09-26-2001, 02:24 PM
G-Benz's Avatar
Razorback Soccer Dad
Join Date: Apr 2001
Location: Dallas/Fort-Worth
Posts: 5,711
Just a guess, but...

...perhaps your idle mixture is too rich?

...catalytic converter is clogged?

...O2 sensor is picking up some chemical byproduct as a result of the plastic bag residue still burning on the cat?

Not sure whether those conditions will send a warning, but it's a thought...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
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Old 09-26-2001, 02:39 PM
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smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
On a 91 300SE, there are maybe a dozen reasons for a check engine light. I got a check engine light for starting the car with the air temp sensor disconnected... or whatever that thing is at the snorkel of the air cleaner.

You can check the code behind the check engine light. Check the archives for the website that tells you how to check the code and how to erase the check engine light when you've fixed the problem. I went to the dealer and they were kind enough to check for me (no tools required). They were also kind enough to shield me from what they were doing.

91 300SE
81 300SD ... buy me
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Old 09-26-2001, 05:27 PM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,768
Check eng light is a heads up for Engine emmision management
system fault.
As last post states, there are several abdcode can be read to give the general area of fault.

Here are the codes that will trip light:
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Old 09-26-2001, 06:31 PM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
Thanks guys, I disconnected the - battery cable to reset the light, and it hasn't re-appeared since.

I cleared away any remnants of the burnt plastic on the catalytic converter, that I assume was causing the problem. It was maybe sending some bad air to the O2 sensor as a previous poster mentioned.

Thanks again!

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Old 09-26-2001, 09:16 PM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
isn't it there is a corresponding message that can
be retrieved when the check engine light comes on?
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Old 09-26-2001, 09:46 PM
pmizell's Avatar
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
Yeah Joel, the code can be retrieved and identified, but was hoping to avoid that cost by posting here. BTW, the check engine light came back on.

Anyone know what the ballpark is for getting the code for this check engine light problem? My guess would be the O2 sensor but wanna make sure before I spring for one.


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Old 09-26-2001, 10:52 PM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,768
If you are handy, you can make a tool to pull codes for $4
worth of parts from RS.
I contain the parts in a clear plastic film can so you are able to see the led. Use the removable top to mount the switch. Bring the test leads out a hole in the bottom.
Fits in your hand nicely.

Here is the wiring set-up.

Code retrieval is key on , hold button 2-3 sec., count flashes,
repeat step 1 to continue on to next.
To clear code , hold sw 8-10 sec. after each code .
No flash or 1 flash means no codes stored.
Disconnecting the bat to get rid of the ck eng lite serves you no purpose [ except temp putting the lite out] . You want the code to see why the lite came on.
There are pulse code retrivalinstructions better than these in the archive. Use search eng.
Or any ????? on the tool, you may email me.
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Old 09-26-2001, 11:41 PM
Dirty Ern
Posts: n/a
My daughters 190E 2.6 (engine's probably close to the 300E) had a check engine light on, and the smog check guy found the tube that connects to the EGR valve was plugged. The tube is about 1/2" OD and goes from the valve around the back of the head and connects under the intake manifold. He disconnected the tube at the valve and started the engine and felt for vacuum on the tube, and there wasn't any. He took his air hose and gave the tube a couple of good blasts and the engine sputtered a bit and the tube was cleared, he cleared the code and the car passed the smog test. I'm sure the plastic bag wouldn't have anything to do with this scenario, but this might help Cap'n Carageous.

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Old 09-27-2001, 08:58 AM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,768
That is a common problem on these and SB has a good article
on that blockage w/pics. in the archives .

As one can see from your post, the mechanic got the code [ prob
egr ], found the problem in the egr system,, reset and cleared the code . Now it is fixed.
That is the procedure.
Not just turning off the lite.
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