94 C280 Check Engine Light issues

[DavidF.C280]

Hello Everyone,

First Time Poster, but I hope to be more active I just found this board :-)

My Problem is with the Check Engine Light which Keeps coming on, so you know its a 94 C280 with 98K. This has been a Problem on and off for the past three months, here is some background.

CE light Came on, and my then mechanic replaced both O2 sensors, in less than a week it was back on again. He suggested the EGR valve, which had already been replaced under the service Bulletin, but would give no guarantees as to wether this would solve the issue, Or in other words he was asking $700 (O2 Sensor and EGR valve R&R) for a "Maybe".

So it was off to the Dealer, they were getting the same codes O2 sensor and EGR, as well as a cylinder 1 misfire, but they replaced the Air Flow Control Valve/Sensor (Will double check but I am 99% sure that was what they did) and put on new plugs and leads. cost $1000. Its Ten days later and the light is on again. Its Booked to go into the dealer on Thursday 10/12. Just so you know I am in the DFW area

To sum up I have two questions.

1. Any thoughts on what could be the problem the EGR valve is the only thing that has not been replaced, but as I said it has been replaced before.
2. I have yet to discuss this with the Dealer, but in your opinon do I have any recourse with them if they charge me full whack to do what they diagnose this time. IMHO I am paying dealer rates ($100+ per hour) I should get the service to match.

All Opinions/Flames welcomed.

David

[mbdoc]

Sounds like they're guessing & not testing. Of course the first thing to check for is a bad engine wiring harness. Look for insulation falling from the wiring. When the computer checks the EGR system it looks for vacuum drop in intake when the valve is energized. Make sure that it is tested. There are about 10 different O2 sensor codes, so what exactly was the code?? It should start P0 ??? or P1 ???.

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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 16V ITS SCCA racecar

[DavidF.C280]

Hello MB Doc,

And thanks for the rapid reply!!

Now this is Interesting, I will give you the full mechanic Report in a second, but first some more info (Dont you hate it when people only give you half the story, sorry!!! :-)

The Wiring Harness was replaced in Oct 99 for the exact issue you described, My Independent shop found it and suggested I took it into the dealer. The Dealer took it in, but claimed not to be able to find any flaking, It took then calling the other shop to find it! They then took care of the Bill for replacing the harness but did charge me $70 "Diagnostic" I did dispute it, esp. as they had to call the other shop to find it! But I thought theres another day! Then the dealer got taken over earlier this year and it is the new owners I now work with.

As you said I felt the first shop I took it to with this (the independent one that found ther wiring harness issue) was "Guessing" which I why i took it to the dealer again.

Here is the full report from them:-

Peformed Engine Checks and adjust. Checked DTC's has P0400, P0301 & P1131. Checked EGR function, Checked Fuel Injection System Checked and replaced Spark Plugs. Repaired Vacc. Lines from Intake to front cover SW/Valve. Checked MAF Sensor and Cleared DTC's. Replaced Air Filter. Test Drove and Checked DTC's and Completed Tests OK.

Hope that all makes sense.

I will mention about the wiring Harness when I take the car in, do you think it could have flaked again?. Let me know what you think, I REALLY appreciate this.

Will keep you updated.

David.

[MikeTangas]

I can't say if this applies to MB, and the Techs will correct me if wrong, but if you keep getting an EGR error code check the vacuum lines to the EGR valve closely.

I had another make which kept getting EGR fault codes, could find nothing wrong with the valve, everything working correctly. Once the code was cleared, it would fault within 100 miles. Very close inspection of the vacuum lines to EGR valve revealed that one line had a "pin hole" leak, which was not noticeable until the line was removed from the vehicle and looked at under bright light. Of course you might not be able to see a very small pin hole, but you could pull a vacuum on the line and see if it holds. This occurred in the 100K mileage range, which is right where you're at.

It's worth a check.

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Mike Tangas
73 280 SEL 4.5

[DavidF.C280]

Mike,

Well the shop called back this morning, and it looks as it you were right!! (I did mention that possibility to the Service Guy when I took it in.)

They got the EGR error code again, and checked the vaccum lines, which had become restricted, cleaned them out, did a 40 mile test drive and it seems fine.

Final Bill - No Charge!!!!, and bring it back in if it happens again. For those of you interested I took it to Park Place Mid Cities Mercedes (formerly Becks)in Bedford-Euless, TX (Just near DFW) they are not the cheapest, but it is one of the Biggest MB dealers I have seen either here or Europe.

Thanks to all for advice and suggestions :-)

David