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Old 10-07-2002, 10:24 AM
Robert C. Eberhardt
Posts: n/a
Angry 1995 C280 - Check Engine(CE) Light on AGAIN!!!

This weekend my wife's 1995 C280 Check Engine (CE) light came on again. This is the third time this has occurred in the last 2 months.

The first time this occurred the computer code indicated a bad coolant temperature sensor and a weak mass air flow (MAF)control. Both were replaced and all was well for 5 weeks after which the CE light illuminated itself again. This time the dealer determined the engine wiring harness required replacement. Well, two weeks after replacement of the engine wiring harness, the check engine light came on AGAIN after a short trip across the street from one shopping center to the other. In a matter of fact, each time the CE light came on it was after a very short trip of a mile or less. Any thoughts on what this could be? One thought I had was a bad O2 sensor. Could that be?

The car has 73,500 miles and the O2 sensor has not been replaced. Has anyone else had a similar occurrence? Before I go back to the dealer again (I am beginning to feel like I live there between the problems with my 2000 ML 320 and the 1995 C 280) I would appreciate anyones thoughts to make sure the problem is corrected at this visit.
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Old 10-07-2002, 03:30 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,503
What code are you getting?

Your experience sounds like mine a year ago, and I did everything you did, and the problem was a blocked egr tube. They get clogged up with carbon from egr vapors.

All M104 engines have this weakness, and these hot inlet pipes need to be reamed out about once every 60,000 miles.

Stevebfl, Steve Brotherton of Continental Imports, wrote a nice article on the home page that details this process:

You should have a code for low egr flow, because the carbon blockage restricts air flow to the egr valve, and a code is tripped, thinking the egr valve is stuck shut (or open), but if it was stuck in the open position, your car would idle badly.
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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Old 10-09-2002, 09:36 AM
Robert C. Eberhardt
Posts: n/a
I have an appointment to visit Mercedes service a week from this Friday so I do not know what codes are stored in the computer. I was just wondering if others had similar experiences that might indicate a common problem.

Last weekend I told my wife the car was idling like a 4 cylinder (not as smooth as usual but not horrible either). Your suggestion that it could be a partially blocked EGR tube could be the problem. For whatever reason, this may trip the CE light when driving short distances of less than a mile.

Thanks for your comments!
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Old 10-12-2002, 07:27 PM
Senior Member
Join Date: Sep 2002
Location: New Jersey, U.S.A.
Posts: 2,398
Hi Robert A blocked EGR tube will NOT cause the engine to idle roughly. If the EGR valve is stuck OPEN it will cause rough running. I'm not too surprised to hear that you've had multiple CE lights though. I've seen o2 sensors, MAF sensors, ignition suppressors, purge valves, assorted vacuum leaks, transmission upshift delay elements, wiring harnesses, etc. cause CE lights on cars like yours. The good news is that 99.9% of all CE lights are EASY to diagnose by any competent MB tech. Following any repair, the vehicle can be road-tested and the repair verified by re-checking the system with the same computer used to check for codes in the first place. Depending on the code and the repair, the tech should know under what conditions to drive the vehicle so that the OBD system performs the req'd self-test for the particular repair that was made. I know it sounds complicated but to an experienced tech it's a piece of cake. Good luck
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Old 10-23-2002, 10:26 AM
Robert C. Eberhardt
Posts: n/a
Question CE light update - 1995 C280

Mercedes techs checked the computer codes that indicated a problem with crankshaft positioning. They also indicated that it apppeared this was caused during operation at higher elevations which makes sense since each time the check engine light went off it was while operation in the North Carolina Appalachian mountains around 3,700 feet above sea level.

Well, the bottom line is several issues can cause this to happen and I guess it is trial and error from here. They indicated that it could be the crankshaft positioning sensor which is a 3 hour labor job to try trial and error fixes. I hate to authorize repairs if this ends up not being the problem and we have to go on from here. This could end up being expensive if we do a try this and try that approach. Anyway, for now I guess the car will be fine if we do not drive it at higher elevations.

Has anyone experienced a similar problem?
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Old 10-24-2002, 05:44 PM
Senior Member
Join Date: Sep 2002
Location: New Jersey, U.S.A.
Posts: 2,398
Thumbs up

What kind of MB dealer uses trial and error as a diagnostic technique?!?!? As a certified MB tecnician I would be embarassed to tell a client I had to guess what was wrong with their car. They are the factory trained professionals( but it sure sounds like they're not acting like it ). When I hear a story like yours it makes me crazy!!! I've attended MB training regularly for the last 14 years and I wouldn't dream of asking a client to roll the dice when it comes to repairing their car. I have explained to more than one person that the problem with their car was elusive, but all I ever needed was time to hunt it down. As far as replacing a crankshaft position sensor being a three hour job, that's just plain insanity! One allen screw, one electrical connector, easily accessible, twenty minutes tops!!! If you can provide me with more information I can probably help you out. What codes are present? And more importantly, how many times did each code occur? Any MB tech worth a darn can easily pull that info out of the vehicle with their diagnostic computer. Perhaps they would be willing to give you that info in order to help you help them. CE lights are NO BIG DEAL. I've fixed hundreds of them ( all on MB's ) and only had a handful that drove me nuts( but I fixed those ones too ). Don't stand for this treatment one minute longer!!!
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Old 10-25-2002, 09:51 AM
Robert C. Eberhardt
Posts: n/a
Sorry, but I cannot help you concerning what codes were read since the dealership did not provide me with this information. Since my wife was considering a new 2003 Mercedes I sure hope they were not using this story to steer her to buying a new car!!!

As I said, this is the third time the CE light has come on. The first time they said that the code indicated a failed coolant temperature sensor and the technician said he drove the car and detected a "weak" mass air flow sensor. This was replaced for a cost of $648. The second time the CE light came on the car was still running fine but they indicated the the main engine wiring harness was deteriorating and needed replacement (a $1,200 repair that Mercedes offered to pay half as a "good will" issue). Now we are here with the CE engine light on again and they can't tell me still what is causing this issue. It appears that the first two repairs were not the REAL problem and it makes me feel that these "Mercedes Trained" technicians really do not know what they are doing or they are behind on there income budget and are looking to meet budget by doing unnecessary repairs. I've told my wife that why would you want to buy another Mercedes if they can't fix the one you have.

I hate to mention names but this is Leith Mercedes in Raleigh, NC. Right now they have cleared the computer codes and reset the CE light and I have the car back. I might take the car back to the mountains so the CE light comes back on and take it to an independent MB tech who I know and trust. In some respects I feel like getting rid of this car and getting a brand that is more reliable and where the techs can fix their cars!
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Old 10-25-2002, 11:12 AM
G-Benz's Avatar
Razorback Soccer Dad
Join Date: Apr 2001
Location: Dallas/Fort-Worth
Posts: 5,711
Unfortunately, your car isn't the ILUVMILS stated, the inept techs working on your car ARE!

I would too be frustrated if I had a problem and took the car to a reputable dealership, only to spend lots of $$$ and see the problem reappear repeatedly.

This should have been fixed the first time and for good (and for probably a lot less money).

Don't sell the car, there's nothing wrong with it. Find another dealership...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car
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