P0299 Fault Code, Please Help!

Hi all,

Firstly hello as I'm a new member! Yay!

Now moving on....lol

I have 2009 Audi A3 2.0 tdi..........With a problem.

The other day I was running really low on diesel so I was on the way my the pumps to get some, as I was on a dual carriageway doing approx 70 in 6th at 2000rpm ish my glow plug light came on and started to flash.

Instantly the car lost power (limp mode) and the glow plug light continued to flash it's self silly. The car was still drivable but felt like there was no turbo boost, and was just like driving my other halfs 1.2 fiesta!.

I made it to the pumps, re-fuelled, turned on the ignition again and all was good. I went around town in the car, Did some short runs (never going over about 50mph) and it was all ok. I'm not a slow driver and tend to give it some red line once in a while and still the car was fine.

A couple of days later while going to work,(again doing about 75 at just over 2000rpm) the same thing happened. I pulled into the hard shoulder, switched the ignition on and off and again all is well. Once I've done this reset it's as good to drive as ever. It's not burning any more diesel then usual so economy is unaffected, it's not making any whistling sounds, there's no smoke, there's nothing apart from this intimmitent fault.

Again it doesn't do it all the time while at motorway speeds but 7/10 times it will.

I gave it a thrashing for about half a hour ragging the bejesus out of it and it performed great, boost was there and the light stayed off.

I decided to take it to a garage to let them have a look, but on picking the car up I'm not 100% sure I think there diagnostic is right.

They say the fault code is P0299 turbo underboost, and they have said that there is a turbo hose that feels a bit soft and they told me there double walled and it may have collapsed inside. However, when I'm thrashing the turbo there's no lag, no nothing it drives faultless, it's only when I'm not really even in the turbo just cruising that this light comes on and the engine goes into limp mode, so I find it hard to believe it's the hose??? And I begrudge paying £150 for a job that didn't need doing.

Has anyone experienced anything like this? Or can anyone shine any light on the situation?

The engine is the CBAB 2.0 tdi.

The car has full audi service history including cambelt and water pump dome 6 months ago and I change the oil every 4 months so it's pretty pampered and hasn't been abused.

Thanks in advance

SmithyAG said:

If the hose has collapsed internally then driving at a cruising speed, then the small amount of boost being created may not be enough to force the pipe open, and the ECU see's not enough boost reaching the engine and logs an underboost fault. When thrashing it and the turbo produces lots of boost, then the pipe may open up and allow it through.

Really you want the pipe off to inspect it, which I would have expected the garage to do, depending on access.

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Thing is wouldn't this show doing a standing test where rpm is the same? Also when at the same rpm else where for sustained period, no issue, only at motorway speed.....and they didn't inspect it, they just told me it felt soft......and charged me £30 for the privilege lol.

SmithyAG said:

The problem with revving the engine in neutral is the lack of load on the engine. This means there is no requirement for boost.

2000rpm in 6th at 70 requires a different amount of boost than 2000rpm in 4th at 50, so it may be that it only detects the underboost under certain circumstances.

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I know what you mean, Im not that mechanically minded, Its just when I've googled the code nothing ever about the hose came up, it was different stuff, and I just don't want the mechanic to be clutching at straws and then charging me for the privilege.

Again I can drive it all day around town and give it some beans and it's all ok, but as soon as it's sustained at 2100ish rpm it decides to go into limp mode.

Hi again

I gave the audi with the problem to another garage,

They couldn't identify the problem, but admit there is one.

They have told me that warranty will cover anything mechanical apart from hoses etc (so turbo and vacuum aculater thingy are covered) so are the injectors etc.....however.

They need to get a proper diagnostic person in and it's £95 a hour, they will cover the price of the diagnostic if it's mechanical but if it's not it's me to root the bill. :-(