Limp Mode - Boost pressure P0299

[coursie77]

Hi,

My first post but i am at a loss with my VW Sharan 2015 plate 2.0L TDI.

I have had a Boost pressure problem.  Under load it goes into limp mode.  The garage have read fault code P0299 and so far replaced actuator, replaced vacuum pump, changed boost pressure sensor.  It has been vacuum tested for leaks, exhaust system checked for air flow, EGR function tested.  On test the actual boost pressure only gets to 847mb and not the expected 850mb.  The air mass meter was also tried from a donor car but still no remedy to the fault.

My independent VW specialist has suggested taking to a dealership for further investigation - but that sounds expensive.

Anybody have any ideas?

Thanks in advance

[SirDavidAlhambra]

Might be a duff turbo, carbon build up in the turbo vanes maybe meaning that itââ,¬â,,¢s letting air out or something like that?

I had a garage like that once, they changed everything except the turbo itself. It was like they were philosophically opposed to the concept of a turbo ever being the source of a turbo related problem

ââ,¬Å"When all else fails, if u have tried everything else, then the only solution remaining now matter how improbable, must be the answerââ,¬Â

Others on here will be much more familiar with this conundrum I am sure

[coursie77]

Thanks for the reply - I left the car with them while on holiday and expected the result to be a new Turbo (i am covered by a warranty on that front) but, yes, they do seem to be going down the route of it must be something other than the turbo itself!

[brianh]

I'd be inclined to try getting them to compare that test result (the 847mb one) to a working vehicle of the same type, I would expect 850 is the minimum it should see, and if its not reaching that it only really leaves the turbo or a problem with the air intake system

(if that hasn't been apart already checking it isn't something daft like a carrier bag or similar stuck somewhere in the intake or air filter housing would be a good idea before trying the dealership, though would expect thats already been ruled out by the folks you've taken it to and should have been seen if they have looked at the functioning of the MAF anyway, but worth checking just to be sure before considering taking it to the dealer as it doesn't look like any of that side has been touched from what you've said, though they may have already done so).

It won't cost anything to ask the dealership how much it will be to have a look at it, though doubt it will be cheap if its not covered by warranty.

[johnnyroper]

That pressure reading 847mb instead of 850mb is not an issue as itââ,¬â,,¢s so small, when that reading was taken was it just revving Iââ,¬â,,¢m neutral? 2.0 cr tdi boost to approx 1.5 bar max under load. Have they done any logs to see what the actual out put is when driving? Ideally it needs to be a log as you can see the specified boost to actual boost curve

I assume basics like air and fuel filters have been checked?

Assuming no boost leaks,map,maf and vac system are good it only leaves sticking vanes or damaged turbo.

Boost issues arenââ,¬â,,¢t really that complicated to figure out if you are methodical,I would question the VW specialists diagnostic skills if I was you.

[SirDavidAlhambra]

Sounds to me like theyââ,¬â,,¢re barking up the wrong tree and missing the obvious. Maybe take a quick look at the air filter, however I would have thought the answer to this one woukd be easy for an experienced mechanic to work out.

Instead of clutching at straws and fiddling about with theoretical possibilities in a trial and error sort of way, it might be better for them to think about a more obvious conclusion... turbo.

[brianh]

It wouldn't drive the turbo properly as the turbo is driven off the exhaust. Partially blocked exhaust would impede flow, the flow drives the turbo, hence it wouldn't drive it as it should.

Same applies on the air side as Johnnyroper says above, if it can't suck enough in due to the bits hes highlighted (though you'd hope they checked the air filter it would be wise to be sure!) you won't get the boost as theres not enough air there to compress in the first place.

[SirDavidAlhambra]

Hehe sorry Brian, I edited my post while you must have been tapping out your response.

For everyone elseââ,¬â,,¢s benefit - I suggested originally that checking the exhaust flow was a crazy line of diagnosis but then I realised (as Brian rightly points out!) that the turbo is of course driven by the exhaust gases lol. So maybe not such a crazy thing to check after all 

[Rob112]

Mine was like this and I changed the map sensor and it cured it  , did you check the actuator arm was moving freely ?