Glow plug light flashing and cruise control not working 2.0 tdi 170

[ThePhoenix]

Hi

I have a 2007 A3 2.0 tdi 170 on 95k miles, which, since the injector recall and cam belt change has become a little rough at idle and smells quite strongly of unburnt desiel/oil on occasion. The possible causes of these issues are not my primary concern (though suggestions would be welcome), but I am adding in this detail just in case it may be related to my main problem.

Three times during the last couple of weeks the glow plug warning light a has suddenly started flashing together with a noticeable restriction of power; rebooting the car (turning the ignition off and on again) resets the light and all is back to normal. A non-Audi specific fault code reader at the local garage shows no faults logged. Each time the issue has arisen at something approaching motorway speeds (60 -70ish) and there has been some minor, but perceptible misfiring at some point in the journey; maybe half a second of hesitation etc.

Now I know there are a lot of things that can cause this and my initial thought is a failing egr valve (which I will be taking a look at at the weekend), but on the last occasion I notice that the problem also took out the cruise control system and the ignition on/off trick only fixed the warning light and took the car out of limp mode, but did not solve the cruise problem - this resolved itself the next day.

I cannot be sure that the glow plug flashing was accompanied by the cruise control fault during the first two failures.

Does the link between the warning light/limp mode/cruise failure help to suggest a likely cause for my problem, or can anyone suggest any tests I can do to help isolate the fault, please?

On a separate note, I have always been of the understanding that this model is fitted with a DPF, but with all this recent activity I have taken to looking carefully at the available dashboard warning lights and I can see no evidence of one for a DPF. On this model and this year is it possible that one is not fitted?

Thank you in advance for any answers/suggestions.

[NHN]

170's were all fitted with dpf's on the 8P, even the new 140's seem to have them, the older 140's didn't.

I would be looking at this as a 1st point of check & checking soot levels to see what percentage its at, could also be a faulty sensor, but it requires vcds or the like to look at things properly, so either find someone local to scan & help diagnose, got a garage or buy vcds yourself as there's only so much a handheld reader can do tbh.

[ThePhoenix]

170's were all fitted with dpf's on the 8P, even the new 140's seem to have them, the older 140's didn't.

I would be looking at this as a 1st point of check & checking soot levels to see what percentage its at, could also be a faulty sensor, but it requires vcds or the like to look at things properly, so either find someone local to scan & help diagnose, got a garage or buy vcds yourself as there's only so much a handheld reader can do tbh.

Thank you for this clarification. As I don't have a DPF warning light, does that mean that the flashing glow plug warning is the subsditute indicator? What do you mean by check the soot levels; remove the DPF and do a physical inspection?

Thanks

[NHN]

You need to get it diagnostically checked with vcds to ascertain what readings it is showing for the dpf sensor, this will also allow you to force a regen.

[ThePhoenix]

You need to get it diagnostically checked with vcds to ascertain what readings it is showing for the dpf sensor, this will also allow you to force a regen.

Thanks for this. I'd just googled how to check the soot level and learned that what you meant was to check with vcds.

I am getting more certain that this car has no DPF though, as it has never done anything that seems like a regen and I have just checked the service book and found a section which should be ticked if the car is fitted with a DPF and it's blank. If this is the case, would you have any thoughts as to what the next most likely cause may be?

Can the DPF be seen easily without removing the undertray?

I realise that I should get faults properly scanned, but if there are any obvious checks I can do I would like to do these first?

As the warning light has now reset, the cruise control is back and the car is currently running ok, will the fault code still be detectable?

I appreciate your help, thank you.

[NHN]

Every single 8P 170 I have known has had a dpf fitted, if yours hasn't then its an anomaly tbh.

Just find someone local on the vcds map to login to the car for you, you cant do much else anyway, as to diagnose the issue you need to see whats faulting & it may have logged the fault already.

[ThePhoenix]

Had it scanned by a very kind member I managed to contact, as suggested. The actual error reported is "Boost pressure regulation control range not reached, intermittent".

We spent a good two hours monitoring the running of the motor with vcds (I say we, I was there, but Tom did all the work ), during which time the car behaved impeccably and did not miss a beat!

Certain things are are recommended to look at: the N75 valve and its piping; leaks in the boost pipework etc. Today I have been doing some of this checking.

I have found something that I think MAY explain this intermittent fault: putting the swirl flap actuator under vacuum has no effect. in fact air can freely be sucked through it. My reasoning that this might be the cause is that if when it is commanded to actuate it just passes unrestricted fresh air into the vacuum pipework this must have an effect on all other functions relying on a good vacuum - including the turbo actuator.

Any comments?

In any case it seems to need fixing. Anyone know if it can be separated and the diaphragm replaced? And for Icing on the cake does anyone know the part number, or at least what it is officially known as?

Thanks all

[NHN]

So basically underboosting.

Afaik the 170 turbo has an electrically controlled actuator, not vacuum, are you saying you've got vacuum controlled unit?

[ThePhoenix]

So basically underboosting.

Afaik the 170 turbo has an electrically controlled actuator, not vacuum, are you saying you've got vacuum controlled unit?

Not sure what which you were saying you thought electric, so here is what I believe to be the turbo actuator, with the control valve and the shared vacuum pipe (arrowed) leading what I am thinking is a swirl flap actuator (next pic):




Swirl flap acctuator?:




And the same again, from a different angle, showing an associated oil leak:



Do you think my theory could hold any water?

Thanks

[Crasher]

Apply a vacuum to the turbo actor and the swirl flap actuator individuals, both are prone to failure. Ignore the flap shaft oil leak for the time being, they all do that, sir...

I had one with a leaking turbo actuator the other day and to my disgust found you cannot buy the actuator and you have to replace the complete turbo, the manifold flap actuator is £11.94...