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Traditional on-going festive season car problems - overboost codes - help?

Discussion in 'Audi S4/A4/A4 Cab (B7 Chassis)' started by Liam198Three, Dec 30, 2013.

  1. Liam198Three
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    Liam198Three New Member

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    Hi everyone,

    Just wondered if anyone can provide any advice on overboost fault code 16618.

    My 2006 (55 plate) A4 2.0 TDI S line Avant has had a series of problem since purchasing it in October, with the following remedies taken so far.
    1. Blown pipe on EGR - Replaced with new EGR cooler by an independant Audi Specialist in Novemeber, no further issues.
    2. Intermittent loss of boost (and power) and occasional black smoke week before xmas - got permanent fault codes for MAF, and glow plugs. Replaced full set of glow plugs and new bosch MAF. Ran fine for short period, then same problems returned.
    3. Looked at EGR valve bit carboned up, and flap was stuck and snapped off the shaft - EGR valve replaced last week. - ran ok for a short time, then keep getting loss of boost, no smoking however seriously down on power, and got engine light on dash - just been to have fault codes read again, and its giving the 16618 overboost fault. Car run ok(ish) for a while after switch off/ restart but then boost drops right off again. Also, after a restart, whilst boosting getting a slight but distinctly noticeable dump valve style flutter when come off the throttle, which isnt normally there. We have looked at the turbo, vanes all seem to be free and fine, actuator lever for the vanes seems to be working ok.
    My mate is having it back in for a look tomorrow, but in the meantime, can anyone give us any further advice or a steer on what it could be or what else to check? Im getting a bit hacked off with the Audi i bought for reliability, and need it sorting before i go back to work and start putting the miles on it again next week! Any help would be massively appreciated, thanks in advance.

    Regards, Liam
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  2. lynallbel
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    lynallbel Member

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    I would defo look at the turbo again, mate has same prob with his gold tdi a few years ago and it was sticky vanes, ign off an on again would be fine until it needed to pull hard again, then light would come on again.
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  3. Liam198Three
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    Liam198Three New Member

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    We had a good look at the vanes today, they seem to move completely freely, and actuator mechanism appears to be working when the car is revved etc. Think the issue lies somewhere else.
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  4. lynallbel
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    lynallbel Member

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    What tells the actuator to move?
    Older cars like mine have a pipe straight to the inlet manifold
    Newer stuff has the same, but has a valve in the air pipe for more precise control
    The very latest stuff is all electronic controlled.
    Im thinking along the line of its its overboosting the actuator is not moving, because its not being allowed/told to move.
    #4

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