2005 BKD 16683 Boost Pressure Regulation/underboost

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thomp1983

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Evening all,

A friend who now owns my old 2005 a3 tdi with the bkd engine is having issues with fault code 16683 which is boost pressure regulation/underboost.

The issue only occurs once the car gets warm, whilst cold it boosts fine.

Today we fitted a recon turbo as the original unit was making a whirring noise and had some play in it.

That hasn't resolved the issue but when looking at an actual vs. requested log the turbo is behaving correctly, it will overboost slightly when you first apply wide open throttle then it tracks the requested nicely, it will kept doing this until it gets warm then the boost goes and the fault code is logged, if you stop and restart the car again the boost will come back for a bit but then goes again.

I've smoke tested the pipework both from the intake into the turbo end and from the boost pipe that attaches to the egr delete on the inlet manifold, there are no signs of leaks but thay didn't rule out a leak under pressure.

All the vacuum hoses appear in good condition, is there a way of testing the pressure transducer that all the vacuum hoses are attached to?

The car has an egr delete fitted with the cooler fully removed, this has left 2 vacuum hoses that have been blocked off. The ecu has been remapped for this.

Does anyone have any other idea of anything to try or a way of testing the pressure transducer as unfortunately there expensive to buy as a guess.

Thanks
Chris.
 
Check the intake manifold flap internals for broken teeth, also check maf readings & the solenoid valve block, make sure the 2 vac lines are indeed sealed 100% & check the boost pipe seals to the IC & turbo, clean any oil, grit in the connections as sometimes the green seals need replacing.
 
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This has the metal intake manifold fitted so I don't think it has the flaps.

He's managed to find a known working pressure transducer for £30 so we're going to fit that and replace all the vac lines for new silicone hose, after that it can only leave an issue with the boost pipe connections
 
No there is an intake man flap that goes before the manifold, it's known for teeth to break, might be fine but something to check.

Check it's moving fully back & forth via diagnostics & take the cover of & inspect the teeth directly.
 
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Sorry yes I see which one you mean, it was replaced not that long ago with a new one as it failed.
 
Iirc there's a a reset option yes in vcds, check under adaptation or basic settings in engine 01.

If it was faulty & wasn't opening properly & new one isn't calibrated it will present similar issue hypothetically as it doesn't know it's stop points.
 
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Hi so had another chance to have a look at this today,

IMG 20260224 135948


That's the fault code as seen in vcds,

IMG 20260224 135536


IMG 20260224 135523


Looking at both the basic settings and adaption screens I can't find anywhere to calibrate the intake flap as discussed earlier in this thread.

He's changed the pressure transducer and vacuum lines with no difference.

Thanks
Chris.
 
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