2007 Audi A4 2.0 TDI, Turbo Boost Related Issues

[john2k]

Hi Guys,

I am new on here. I have a 2007 Audi A4 2.0 TDI with just over 100k miles on it. On long journeys that take more than 3 hours, the car goes into Limp mode, the MIL turns on and the Glo Plug light illuminates. If i let the car sit for a while, then it comes out of limp mode and everything works fine. Strange thing is that it never happens on journeys under 2hrs long for some strange reason. I've connected up VAG-COM and read the codes and 4 error codes exist on the Engine module. the codes are:



P0234 Boost Pressure Regulation: Limit Exceeded (Overboost Condition)
P0113 Intake Air Temp. Sensor (G42): Signal too High
P0238 Manifold Pressure / Boost Sensor (G31): Signal too High
P0243 Solenoid Valve for Boost Pressure Control (N75): Malfunction




Can this be 4 seperate issues or could it be one issue causing 4 different codes? Any idea what to look at?

Any advice would be greatly appreciated.

Thanks

[Alan02]

The N75 valve controls the boost. The Variable vanes at the turbo react to what vacuum it recieves from the valve. Check contacts at n75 and check for sticking mechanism at turbo.

[Crasher]

There are three common possibilities for the limp mode from the over-boost situation, a clogged up turbo (by far THE most common reason), an over sensitive Manifold Absolute Pressure sensor (VAG called it a Thrust sensor) and a sticking N75 valve. Interestingly the Thrust sensor is the MAP (G31) sensor AND the Intake temp (G42) sensor combined which does suggest that changing the Thrust sensor first would be a good decision if no skilled mechanics were available. If this fails to stop all of these codes, then some deeper investigation would be required and a common problem I have seen is the wiring to the N75 valve breaking because it was routed badly from new. A proper VAG specialist would be able to carry out some direct Basic Settings and Outputs Tests to determine what is going on without any trouble or throwing parts at it will nilly.

[john2k]

Thanks for the replies. Considering the mileage and age of the car I am considering changing both the N75 valve and the MAP sensor. Are these components easily accessible? Is the MAP sensor just connected to the intake pipe? and where will the N75 valve be and is there any special procedure to replace the N75 valve? is it just matter of removing the hose clamps and replacing? Any pictures of the location for the N75 valve? The car is 2007 Audi A4 2.0 Cabriolet

[Crasher]

I would say from experience that there is only a 1% chance of a new Thrust sensor or N75 valve curing the overboost problem.

On the BPW and BRC engine, the Thrust sensor is on the plastic charge air pipe as it runs across the back of the firewall after taking a 90 degree turn at the water bottle, check the brown/black earth wire for a break. The G31/G42 Thrust sensor and the N75 are not connected and if there was a supply fault to the N75, you would have V157, N144, clutch switch and glow plug problems. I would suspect that the only true fault code is

16618 (P0234) 000564 - Boost Pressure Regulation: Limit Exceeded

Possible Symptoms

Malfunction Indicator Light (MIL) ON
Boost Pressure too high (in Measuring Blocks 011 zones 2 and 3)
Reduced Power Output (limp mode)

Possible Causes

Vacuum system leak or connection issue
Boost Pressure Control Valve (N75) faulty
Boost Pressure Sensor (G31) faulty
Turbo Charger stuck/faulty

Possible Solutions

Check charge pressure control vacuum system for leaks
Perform output test of N75 valve
Perform Basic Setting in 011
Perform charge air system pressure test
Check boost control valve (N75)
Check Manifold Absolute Pressure (Thrust) sensor (G31)
Check turbocharger actuator travel and diaphragm for air leaks

The other fault codes strike me as those devices being messed around with when the engine was running

[john2k]

Thanks for the reply. Is there any particular reason why you would think changing the MAP and N75 would only likely have a 1% chance of curing the problem? considering they represent combined 50% of the possible causes.

[Crasher]

Because I work on these cars all day every day (just taking the clutch out of a 2006 8E at the moment and just put the turbo back on a 2008 8K yesterday) and I hardly EVER buy thrust sensors or N75 valves for any VAG car, in fact I think the last N75 valve I bought was at least 2 years ago and the last thrust sensor was for a petrol engine, before that I can't remember. Every single time I get this fault code it is a sticky turbo vane ring/vanes. The other fault codes are the 1% hesitation for me but I suspect they are small red oily fish......

[Bradderz85]

Hello newbie here sorry to jump in the post haven't got a clue how to post on here or where to post but I'm having vacuum trouble with my 04 plate a3 2.0 tdi it doesn't seem to boost up properly in 1st and 2nd gear just seems to hit a wall but if I ease off and on again it kicks in properly , experimentally I took off vacuum resivour pipe and it cured it for a while then I think it must have lost all vacuum and went limp I put resivour pipe back on and ten minutes later back to only being no good in 1st and 2nd any help would be much appreciated also at idle if I accelerate it only goes to a certain point just like in 1st and 2nd but if I go off and on accelerator again it will hit the guv'nor ?????? I'm lost any help greatly appreciated

[terryjippo]

Because I work on these cars all day every day (just taking the clutch out of a 2006 8E at the moment and just put the turbo back on a 2008 8K yesterday) and I hardly EVER buy thrust sensors or N75 valves for any VAG car, in fact I think the last N75 valve I bought was at least 2 years ago and the last thrust sensor was for a petrol engine, before that I can't remember. Every single time I get this fault code it is a sticky turbo vane ring/vanes. The other fault codes are the 1% hesitation for me but I suspect they are small red oily fish......

Sorry to resurrect an old thread, but I have the P0234 issue appearing on wife's BLB-engined A4 2.0 TDI. This ONLY happens though on a cold engine, never once its warm. Crasher any ideas what this might be please? I'm guessing the turbo will need cleaning properly regardless but could that particular issue be caused by a sticking actuator rod?

Cheers in advance for any advice.
Tel

[Crasher]

The rod sticks due to the carbon inside the turbo, for a while it may only do this when cold as when hot the turbo expands and the carbon fouling becomes less of a problem but it will eventually do it all the time.

[terryjippo]

Thanks for the message, I suspected as much. Bring on some dry weather to do the strip down! Cheers Tel

[Rocker8742]

Well seeing as it’s already been revived...

I’ve got a BRE engine which yesterday started behaving oddly, no lights on the dash and no early symptoms but anything over 1/4 throttle does nothing apart from throw smoke out of the exhaust unless Iim around 2k rpm. Car was mapped almost a year ago and has been perfect since bar a faulty MAP sensor.

I’ve checked the flexy boost pipes between turbo and manifold and can’t find any splits guessing it could be a vacuum line split but will have to wait for it to cool down to check properly. Any other thoughts on what it could be?

[Crasher]

Possibly a sticking EGR valve, even though you have no warning light on, with that symptom I imagine a code will be stored.

[Rocker8742]

Thanks Crasher I’ll have a look at the codes tonight. No signs of any split vac pipes they’ve still got vac and the actuator moves freely. Out of interest is the hard boost pipe that runs across the front of the car a common failure or are they fairly robust?

[Crasher]

Never known one fail, on that engine I have seen the G28 crank sensor come up as an error but it is a red herring, the problem is actually condensation inside the EGR valve electrics.

[Rocker8742]

Just read the codes and got P0404 EGR “A” Control circuit range/performance, I presume that points towards an EGR that’s either clogged up or got a wiring/electronic issue

[Crasher]

Often the motor is full of oil.

[Rocker8742]

Often the motor is full of oil.

The EGR was indeed very clogged up, cleaned both that up and most of what I could get out of the manifold, cleared the code but it’s still behaving the same as before and after having driven it it’s got the same fault code again P0404

Seems completely randomly it will pick up perfectly fine as normal and then power will just tail off and it feels like it’s being held back

[Crasher]

Did you take the cover off the motor and check for stripped gears and oil contamination. When you take the cover off, put some cloth under it (not toilet paper, too valuable) as they can hold quite a lot of oil.

[Rocker8742]

I didn’t, can’t say I even thought about that to be honest, I should have a whole spare EGR I can try to rule it out though

[Rocker8742]

Swapped for a spare EGR valve and the problems cleared up and driving nicely again. Thanks for the help 👍

[Pover74]

Hi pall seen your thread got audi a3 quattro 2.0tdi sline had all new parts and it's boosting about 20 seconds then going into limp mode but all brand new sensors driving me crazy thanks

[Crasher]

You would be better to start your own thread as most people will miss this, include a fault code report.