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  1. #1
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    Post C63 0775 and 0780 CEL problems (help)

    Hi guys

    posting from Western Australia where I dont have anyone who can solve my problem wtih CEL on my modded c63. every mechanic/shop including the two dealers are hopeless and unfortunately, I am the only person in WA who has modded both exhaust and ECU.

    here is the history

    1. ordered cargraphic headers back exhaust w the cats. mufflers have valvetronic flaps.
    2. sent ecu over to the east for a tune
    3. mercedes dealer i bought the car from agrees to fit cargraphic headers but voided my warranty and made me sign a waiver. they do a shxt job and damage a diaphragm and the overfall fitment is attrocious - I had to fix it myself. they have also damaged the one-way valve from the vaccum canister and vaccum is not held overnight. exhaust flaps rattle and sound like shxt in the morning on start up.
    4. dealer installed modded ecu but gets CEL and cant get rid of it w star tester. rather than fix problem, they void my warranty and tell me the ECU is bad.
    6. after getting frustrated, i buy an OBD reader and read codes myself
    7. codes thrown because dealer has put rear 02 sensors in front and vice versa (?!!). star tester msg even told them that so obviously an apprentice working on my 160k car Click here to enlarge
    8. i take car into dealer, swap 02 sensors to correct position over on their own hoist, clear w star tester, voila, CEL clears. dealer embarrassed.
    9. that day, no problem with CEL
    10. next morning on startup, CEL comes back, this time with a new error : 0775 The signal from oxygen sensor 1 bank 1 is shifted towards Lean 0780 the signal of oxygen sensor 1 bank 2 is shifted towards rich. car running very, very rich and i can smell the excess fuel. have tried clearing with star tester and the CEL clears and doesnt return that day, but again comes back the next morning (after all vacuum leaked).
    11. swapped all 02 sensors out, cleared CEL with star tester, same deal: 0775 and 0780.

    is the problem due to:

    1. the dealer not takign vaccum off the right point? maybe one bank and not the other?
    2. is it the ECU? has the tuner made an error when disablign the rear 02 sensors to stop the cargraphic throwing CEL?

    please, if anyone knows how to fix this, I would really, really appreciate some help.

    thanks
    frustrated_c63

  2. #2
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    wow, what a nightmare!

    First get your vacuum leak fixed. Also, verify that the o2 sensors are indeed in the correct position.

    One other thing you can try is removing the power from the battery for a bit and "rebooting" the car. Sometimes these cars have strange gremlins that stick around.

    Incorrect disabling of the o2 sensors through tuning does happen. I would also tell your tuner what is happening and see if they have seen that on their code before.
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    Well I would probably normally say that the 02 sensors are swapped left and right side but I have actually done this intentionally on the c63 and it knew that I did it. I would tend to think that it is an issue with the tune also. It is really hard to create a bank specific vacuum leak. You might check the purge valve though these go bad a lot and can stick open pulling fuel vapor all the time. Again though this is not bank specific but worth a shot.

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    thanks guys

    yeah, you get a different CEL if sensors are swapped for L/R plus the car will misfire and run like shxt.

    it must be the tune. ill send it back to him and if no good, will try MHP.

  5. #5
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    go to mhp there tunes are the best my friend

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    Click here to enlarge Originally Posted by malooamg Click here to enlarge
    go to mhp there tunes are the best my friend
    Definitely a quality option.

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