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Offline Oscini  
#1 Posted : Wednesday, December 15, 2010 6:46:26 AM(UTC)
Oscini

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Car came in as down on power and was in limp home mode with no boost. At that time it was showing faults 17965 (P1557) charge pressure control deviation and 17563 (P1155) Map sensor short to B+. I checked the wiring from the ECU to the map sensor, checked the operating arm for the variable vane turbo moved freely under vacuum (moved at 10 in Hg and boost control solenoid delivers 20 in) so changed the Map sensor. Still goes into limp home and cuts boost after a few minute driving (never while stationary) but now only throws up code 17563. One funny thing, when code is there it shows as a static error and will not clear, switch engine off and on again it shows as intermittent and will clear but I think this may be normal once the code is set.
I'm starting to think about ECU problems but has anyone else got any ideas please?
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Offline nelpavakese  
#2 Posted : Wednesday, December 15, 2010 3:26:09 PM(UTC)
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Can you get snapshot data of the moment the code was set?
Or hook a recording scope to the MAP's signal wire and a boost gauge/transducer to see what's happening when it flags?
Offline MarPydayamurn  
#3 Posted : Thursday, December 16, 2010 7:15:05 AM(UTC)
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You could take out the Charge Pressure Sensor (MAP) and apply pressure with Mity vac or similar, look at live data to compare readings with pressure applied, to test the integrity of the sensor and its associated wiring.
If the pressure has been exceeded then you will probably be looking at sticking vanes.
Offline Oscini  
#4 Posted : Thursday, December 16, 2010 4:38:14 PM(UTC)
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Good suggestions, as always, but my scope is away for repair and I'm on my own today so can’t really watch live data and drive it hard at the same time! Tomorrow I may rig up a boost gauge where I can see it and/or grab a willing driver. Even so excessive boost would have given the 17965 code but that’s gone now and (unless I'm messing something) I don’t see how too much pressure could give code 17563. Or could the boost be high enough to push the voltage so high the ECU sees it as a live short? Before the code is set it doesn’t seem to drive any better than I would expect but you can definitely feel the boost go when it goes into limp home.
I'll let you know how I get on tomorrow
Offline Oscini  
#5 Posted : Friday, December 17, 2010 9:24:08 AM(UTC)
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You were both right (of course!), when fault code sets specified manifold pressure is 1,800 mbar and actual pressure 2500 mbar on live data and a pressure gauge. Boost control solenoid is working fine (checked with vacuum gauge as scope still not back) so turbo off tomorrow and no doubt will be posting as fixed later in the week. Still puzzled why it sets DTC 17563 and not 17968 (the infamous P1557) though. It obviously is over boosting but why doesn’t it set the normal over boost code since I changed the MAP sensor? Any thoughts on that would be welcome just for future reference.
Thanks for the replies though.
Offline markingram6  
#6 Posted : Friday, December 17, 2010 6:04:03 PM(UTC)
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When you say you checked the wiring between MAP and ECU, did you check them for short circuit to each other, to B+ and to Ground?
Regards
Offline Oscini  
#7 Posted : Saturday, December 18, 2010 3:02:01 AM(UTC)
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Yes I did it, but only with engine off. For a while I did think that maybe something was happening in the ECU but as it definitely is over boosting, and that is when it sets the DTC and goes into limp home then I now think it must be the turbo. I have just checked it again on the road and from about 2,000 rpm upwards the difference between specified and actual boost gets wider and wider until the DTC sets and all boost goes.
Offline Oscini  
#8 Posted : Saturday, December 18, 2010 4:38:14 PM(UTC)
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All sorted, replaced turbo (after cleaning it in-situ, maybe helped but didn’t cure). I STILL don’t understand the DTC that was thrown up though.
Double checked on KTS and VAG COM, same code.
A lesson taught as I suppose.
As always thanks for the help.
Offline nelpavakese  
#9 Posted : Sunday, December 19, 2010 12:07:04 AM(UTC)
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We always strip and clean these turbos with good success. It is very common fault.
Can't explain the code thing (no surprise there) but I think I've seen the same before.
Offline Oscini  
#10 Posted : Sunday, December 19, 2010 9:38:15 PM(UTC)
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I thought about that Chris but I remember seeing somewhere on here that someone (yeah, vague I know!) had found that the problem returned a few months later so they now fit new. I'm sure your advice is right but for this particular (VERY particular as it happens!) customer I didn’t want to risk that.
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