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Can't nailp0299 turbo issue


I have a 2003 Audi A4 Quattro with CEL of p0299: turbo underboost. I changed the turbo out as well as the pcv valve. I’m not having any luck on what the problem could be or getting it properly diagnosed without paying some ubiquitous 90$ guessing game diagnosis fee. Anyone have a clue on where to look?

Is the waste gate valve working properly?


Guessing a bit, I might wonder about a vacuum leak or the possibility of a turbo overboost valve problem if the Audi is equipped with one.

The vacuum leak could be checked with a vacuum gauge by connecting it to an intake manifold vacuum source below the throttle plates and checked at idle only.

The vacuum gauge could also be used to check for an exhaust restriction.

You changed the turbo out and nothing changed ? That is called throwing parts at a problem. A diagnostic at an Audi dealer will not be a guessing game so why not do that and possibly find the actual problem.

Here’s what it looks like.


Im not sure. I want to have a mechanic look in the right place. The last shop told me it was the crankcase pcv valve. I replaced the pcv valve but wasn’t sure if the crankcase is a separate issue/part.

Inspect the intercooler for damage/leaks, inspect the tubes, clamps and rubber connectors to and from the intercooler for loose connections and damage. Problems in these areas can result in pressure loss.

You bought a new turbocharger, but you’re balking at the price of diagnostic?

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How many miles on it?
Odds are that you’ll spend far more changing parts (up my way we call that “shotgun maintenance”) than the cost of a proper diagnosis. I can understand, however, your reluctance since you got a bad suggestion once already.

For the record, the pcv valve is the “positive crankcase ventilation” valve. It allows the pressure and gasses from the crankcase to be drawn into the engine’s induction system (the inflowing air). The crankcase and the PCV valve are not separate issues, but related. The “crankcase” is not a part, but is the area around the crankshaft that’s enclosed by the oilpan, the engine block, the pistons, and some other parts. There is nothing that has to be done to the crankcase for this issue. The valve and the orifice that it allows the crankcase gasses to be drawn into are the issues the mechanic was directing you to.

Since the code is for a turbo underboost, I think OK4450 is giving you good guidance. He knows engines, and a vacuum leak or plugged exhaust make perfect sense. The exhaust stream is what drives the turbo. and the stream needs to be unimpeded by an unintended restriction and the ducting pretty much intact for the system to work properly.

So it has about 125k miles on it. I’m taking just what you suggest: have the mechanic look at the plugged exhaust or vacuum leak by using a vacuum gauge.

I guess I’m irritated because I did have it diagnosed at the Audi dealership and was told I needed to replace the turbo. Having done that (they performed a test of some sort) I took it to another shop to actually replace the turbo (cheaper by almost $800) So the code came back again. I thought the audi dealership misdiagnosed it. Took it back to the shop and asked for the turbo to be replaced. They supposedly did a test and said the the PCV needed to be replaced (no reason to replace the turbo). Gave me a $900 estimate. Saw a youtube video saying it could be a DIY and not labor exhaustive.

So, I will find another local shop and ask for a vacuum test to pinpoint where it could be. But I just want to make sure that when I take it to a shop, they aren’t futzing around with it and ask them for the proper test. I’ve already been beat over the head financially atleast twice. Here in VA the standard diagnosis fee is 90$ with a labor rate of about 95-100 per hour. I want to get it right and not waste any more money.

You will certainly continue to waste money unless you ask the mechanic to properly diagnose the problem. And stick with a mechanic that you think is best. Jumping from mechanic to mechanic is like being tested by one doctor for heart surgery…then going to another and having him do the surgery, but he doesn’t get to see the test results from the first doctor or do any testing of his own.
But if that’s the way you roll…go ahead…and I do heart surgery on Friday nights. Cheapest around…and I could use a new boat!!!

Taking a car in and requesting the test YOU think is proper is forcing the mechanic to put on blinders and then magically give you a diagnosis. Give him a free hand in the diagnosis.

If the mechanic wouldn’t charge you the $90 for the diagnosis you would go home and use his diagnosis to repair it yourself and he would shortly go broke.
He is entitled to be paid for is time and expertise.

Pay the fee and let someone diagnose it properly.