A4 TDI 170 P0299 Underboost on occasions
Discussion
Wonder if someone could advise.
Basically car had being going great, then after a timing belt/water pump change it was coming up with this code.
Audi fault finding was stopping at the N75 solenoid valve which was replaced.
However it is still happening.
The thing is I can't seem to get it to do it myself but my other half can.
The hoses have all been checked and appear ok.
Have read so many different possibilities, is there a best way to pinpoint the issue, if Audi are coming up with N75 and after changing it's no good, not sure point in trying the same again to end up replacing lost of parts that are not the real issue.
I know the 170 has a reputation for injectors, is it possibly the start of that, is it worth throwing in some reex or similar or is that a no no for this engine.
Any pointers most welcome
Basically car had being going great, then after a timing belt/water pump change it was coming up with this code.
Audi fault finding was stopping at the N75 solenoid valve which was replaced.
However it is still happening.
The thing is I can't seem to get it to do it myself but my other half can.
The hoses have all been checked and appear ok.
Have read so many different possibilities, is there a best way to pinpoint the issue, if Audi are coming up with N75 and after changing it's no good, not sure point in trying the same again to end up replacing lost of parts that are not the real issue.
I know the 170 has a reputation for injectors, is it possibly the start of that, is it worth throwing in some reex or similar or is that a no no for this engine.
Any pointers most welcome
Well she is not the best at explaining or remembering what she was doing when it happened.
She gave me the impression she was in too high a gear at first so I tried pulling for low revs in 3rd, 4th and 5th several time and couldn't get it into limp mode.
Today she said it happened when she felt she revved the car too much on a dual carriageway and thinks she was at the higher end of 3rd
The other garage said they did some vaccum test, sounds like it might be one mentioned.
What would be the next port of call if they did carry out this test
She gave me the impression she was in too high a gear at first so I tried pulling for low revs in 3rd, 4th and 5th several time and couldn't get it into limp mode.
Today she said it happened when she felt she revved the car too much on a dual carriageway and thinks she was at the higher end of 3rd
The other garage said they did some vaccum test, sounds like it might be one mentioned.
What would be the next port of call if they did carry out this test
Called Audi today for few reasons, seen the VOSA bulletin relating to injectors, do you know if this is covered?
This car had one replaced in June, they are saying they will only replace all if another one goes, other opinions seem to differ?
Turns out the car had this underboost fault before and Audi diagnosed EGR, which they never replaced but it was replaced elsewhere.
Obviously it was not the fault as it still happens, again fault finding then stopped them at the n75 which was replaced but it still happens.
Seems this fault finding is a bit of a waste of time, you need to look further than a computer flagging N75 and just go and change it without looking at possible wiring or vac issues.
So assuming Audi would have already done this VAC test when it was in, they didnt confirm this however...maybe the mechanic never bothered!
So over the phone Audi are now saying sounds like Turbo....well first it was EGR...no, then N75...no so now they will go for a turbo, 3rd time lucky, seems a joke they cant pinpoint an issue without replacing various parts first!
This car had one replaced in June, they are saying they will only replace all if another one goes, other opinions seem to differ?
Turns out the car had this underboost fault before and Audi diagnosed EGR, which they never replaced but it was replaced elsewhere.
Obviously it was not the fault as it still happens, again fault finding then stopped them at the n75 which was replaced but it still happens.
Seems this fault finding is a bit of a waste of time, you need to look further than a computer flagging N75 and just go and change it without looking at possible wiring or vac issues.
So assuming Audi would have already done this VAC test when it was in, they didnt confirm this however...maybe the mechanic never bothered!
So over the phone Audi are now saying sounds like Turbo....well first it was EGR...no, then N75...no so now they will go for a turbo, 3rd time lucky, seems a joke they cant pinpoint an issue without replacing various parts first!
That is what I was thinking, easy fix...seems I was wrong 
Any idea of the cost of the Vac actuator and time to replace roughly.
I also asked about any software updates but never got much feedback there, would have thought the applied it when it came in with the fault previously.
I then asked to speak to someone higher up the chain, they sounded more knowledgable, he was reading either the report from the tech if that is how it works or from the receipt, he said something like car road tested no fault found, audi fault finding carried out and EGR found to need replacing as leaking oil.
It was then changed elsewhere, I mentioned the vac actuator but not a lot said on that, I asked if the tech would have done tests there first, he just said I assume so....would be good if he could have answered a definite yes or no.
The N75 was put on after fault finding and was told it was faulty for sure but it's looking like was nothing wrong with it at all
There is no loud hissing so would like to think the boost leak was ruled out, would a small boost leak possible cause, I'm told the hoses are all good, but guess can be difficult to pin point some minor leaks.
This one seems to rev up when I have tried it, I actually tried pulling from 3rd down at 1000rpm several times but couldn't get it to play up.
It doesn't feel like a 170, well it feels like one had before which wasn't limping but seemed gutless, then a couple thousand mile later an injector went.
I will have a go again see if can get it to limp with me as asking the other half and she reckons it has happened at the bottom end and at the higher end.
Whats the cure for blocked injectors, do they need cleaning or replacing or does the likes of Redex make a difference.
Have you heard the official take on the injector issue, I'd rather get all them done too given had one go before and this one has already had one go down.
Meant to say Audi first had the car in with regards to underboost around 5k miles ago, if it was the turbo would it not have packed in completely by now?
Any idea of the cost of the Vac actuator and time to replace roughly.
I also asked about any software updates but never got much feedback there, would have thought the applied it when it came in with the fault previously.
I then asked to speak to someone higher up the chain, they sounded more knowledgable, he was reading either the report from the tech if that is how it works or from the receipt, he said something like car road tested no fault found, audi fault finding carried out and EGR found to need replacing as leaking oil.
It was then changed elsewhere, I mentioned the vac actuator but not a lot said on that, I asked if the tech would have done tests there first, he just said I assume so....would be good if he could have answered a definite yes or no.
The N75 was put on after fault finding and was told it was faulty for sure but it's looking like was nothing wrong with it at all
There is no loud hissing so would like to think the boost leak was ruled out, would a small boost leak possible cause, I'm told the hoses are all good, but guess can be difficult to pin point some minor leaks.
This one seems to rev up when I have tried it, I actually tried pulling from 3rd down at 1000rpm several times but couldn't get it to play up.
It doesn't feel like a 170, well it feels like one had before which wasn't limping but seemed gutless, then a couple thousand mile later an injector went.
I will have a go again see if can get it to limp with me as asking the other half and she reckons it has happened at the bottom end and at the higher end.
Whats the cure for blocked injectors, do they need cleaning or replacing or does the likes of Redex make a difference.
Have you heard the official take on the injector issue, I'd rather get all them done too given had one go before and this one has already had one go down.
Meant to say Audi first had the car in with regards to underboost around 5k miles ago, if it was the turbo would it not have packed in completely by now?
What is worst with yours and what codes do you get?
Advice now is to maybe have the turbo cleaned but no guarantee it would work, any thoughts?
Is there not a way of diagnosing these cars properly.
It just seems to be the same over and over, take pot shots at changing various things, only for it to return.
If Audi guided fault finding says EGR and it's changed yet still returns then surely Audi guided fault finding is a little misguided or is it user error?
Advice now is to maybe have the turbo cleaned but no guarantee it would work, any thoughts?
Is there not a way of diagnosing these cars properly.
It just seems to be the same over and over, take pot shots at changing various things, only for it to return.
If Audi guided fault finding says EGR and it's changed yet still returns then surely Audi guided fault finding is a little misguided or is it user error?
Tame Technician said:
Tame Technician said:
Check the vacuum actuator for the inlet manifold flap.
They split inside and cause a loss of vacuum in the system so other vacuum operated item, like the turbos actuator and N75 solonoid dont have enough vac left to work properly.
Have you done this. They split inside and cause a loss of vacuum in the system so other vacuum operated item, like the turbos actuator and N75 solonoid dont have enough vac left to work properly.
Its very much the likely cause. I had a 170 in only yesterday, had no faults in the memory at all but customer described limp home mode intermitant. With nothing to go on we checked a few things including the EGR valve which was fine, but when we tested the actuator with a mityvac it would not come close to holding a vacuum.
Part is only about £10, need the inlet manifold off to fix, so labour is 1.0 - 1.2 hours.
Edited by Tame Technician on Friday 23 September 18:33
I mentioned it to Audi and said when it was in previously surely the techs would have checked this.....there was silence followed by, I'm sure they would have.
When he read out what had been done (at Audi), it didn't actually say VAC test, it just said guiding fault finding...found problem, change part and voila.
Cheers mate, great information there.
With regards to my talks with the Audi dealership it was not just the basic service advisor, it was someone higher up the chain, forget their exact title but they did seem to know more than your average person that you speak too.
I would have thought they would have covered this avenue as you mention there is a TPI about it, whatever that means
Is there some document available explaining that it is a known weak point
With regards to my talks with the Audi dealership it was not just the basic service advisor, it was someone higher up the chain, forget their exact title but they did seem to know more than your average person that you speak too.
I would have thought they would have covered this avenue as you mention there is a TPI about it, whatever that means
Is there some document available explaining that it is a known weak point
Tame Technician said:
Technical Product Information.
Audi are very funny about releasing information about known faults. I really cant upload the details of the TPI on here, or anywhere on the internet. If I can find it somewhere else with google, because I know what words to search then i would do so but I cant for this one. The TPI basically details the likely causes of P0299 and advised tech how best to fix it. Including the test on the manifold flap actuator, and if everything checks out ok the required SVM code to update the software in the ECU.
The actuator is something silly like £9 or £12 i cant remember. Take about an hour to fit.
DO you know nayone with a Mityvac?, test it yourself???
Cheers for all the info TT.Audi are very funny about releasing information about known faults. I really cant upload the details of the TPI on here, or anywhere on the internet. If I can find it somewhere else with google, because I know what words to search then i would do so but I cant for this one. The TPI basically details the likely causes of P0299 and advised tech how best to fix it. Including the test on the manifold flap actuator, and if everything checks out ok the required SVM code to update the software in the ECU.
The actuator is something silly like £9 or £12 i cant remember. Take about an hour to fit.
DO you know nayone with a Mityvac?, test it yourself???
Your good self excluded, are Audi techs known for not knowing the full info regarding TPI's, guess they have to be bothered to go and read the info in the first place?
I managed to talk with 2 master techs and both didn't have a clue what I was talking about, doesn't put your mind at ease at all, then one went and checked up and came back saying it mentioned it along with possible dirty injectors.
One dealership said you cannot speak to any of the techs.
Was hassle getting the part too, parts didn't have a clue but managed to talk to someone in TPS who located the part on the system as 'vacuum unit'?
Indy garage changed it but charged a lot more than 1 hour, so far not had boost fault....but then it wasn't happening with me before, need to get the wife to do some driving
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