Hi everyone,

I have been driving my Audi A4 B9 2.0 TDI for nearly 2 years now and recently I started to experience a fault on my dash. When I scan it on my diag tool it comes up as Fault code P0045 Turbocharger/Supercharger Boost Control "A" Circuit/Open. It is quite random when it comes up. Sometimes it comes up after driving around 15 mins when the car is fuly warmed up and sometimes it comes up after around 5-10 mins when the car is halfway warmed up. Most of the times it comes up when it is properly warmed up and I have driven it for more than 20 mins. When this error comes up on the dash it appears as a yellow warning sign on the dash and the car goes into Limp mode. There are no weird noises from the engine bay or anything at all to lead me to believe that it could be a mechanical issue. I have been adviced by a garage to try and drive the car on motorway to try and clear the turbo from any soot build up. I drove around 1-1:30 hours no stop holding between 2200-3200 rpm most of the drive and even after that the error code still comes up. When the car is switched off and back on again for around a minute the error goes away but most times it comes back shortly after. I have done some research and it appears that this part (6nw 009 420) could be the cause of this issue but I am no mechanic and I am not sure if the car even has this part. I believe the car still has a DPF.

I am not sure what else I could say about this issue to help give an idea of what it could be but if there is anyone has questions that I can answer to help narrow it down, it will be appreciated.

Thanks

Ideally I would try and scan with VCDS to narrow down the issue before you fire the parts cannon at it. My understanding of that error code is low voltage at the turbo actuator, whether vacuum line or boost solenoid. I had an issue with the turbo on my old A4 Allroad 2.0 litre diesel (177PS) at 70k miles that I traced to the actuator. It's actually pretty specialised to replace just the actuator, and to be frank, on a 2015 car, then there's likely to be carbon build up on the turbo on the vanes. I replaced with genuine Garrett turbo from these guys rather than pay daft money to Audi. It's exactly the same part. https://turbo-diesel.co.uk/. Now you're not at that stage yet. If it is the turbo, then replace the oil feed line too, that bit is crucial, plus oil change, etc.

You can cross reference parts via LLL Parts and take it from there. I tend to run Forte diesel conditioner through it if it throws a code. Drive hard, then swap out the fuel filter afterwards.

Does your car have a N75 valve?

Hi again and thanks for the reply.

The first thing I am pretty sure is that my car doesn't have a N75 valve due to it being a B9. Using VCDS is not an option for me since it is quite expensive and I am just trying to see what the issue might be due to me selling the car. I no longer drive it but I have attempted to find the solenoid that could be causing this issue but to no avail. I have tried the method of hard driving the car for a long period of time and that didn't solve anything. I forgot to mention that the car is at 162000 miles mostly driven on motorway. Oil changes have been done every 5000 miles too. I am no mechanic and I am just seeing if I could fix it myself but if it's something big like having to replace the whole turbo, I could't do that job. I don't think it is the turbo itself, due to it being very responsive and having no loss in boost. I am pretty certain that it is an electronic issue. I am sure there are application out there for mechanics that show you a diagram of all the components in the engine bay. It would help if I had it to see where this actuator might be located on my car if it even has one.

Not sure where I got 2015 from, it might have been on your signature, or I was replying before I had my Weetabix! Good news on the 5k oil changes.

Search LLL parts. It has diagrams for parts based on year and engine code. There's always pay to view ErWin too, however without a full diagnostic, it would be difficult to pin down exactly what youre looking for. Audi independent might be logical next step.

Yes I think I’ve put the model and year on my profile. In terms of LLL parts I could not find my exact model on it and I am not really sure what I’m looking for on there either. And the other website ErWin looks complicated and same over there not sure what I’m looking for as well. Thank you for trying your best to help but I am not too familiar with using any of these websites and was just seeing if anyone had a similar issue but it proves a little difficult to find out the exact cause of the issue without someone with knowledge looking at it personally. I will probably leave this topic open just for future in case someone knows something that we don’t.

Thanks again

Update:

I have done some testing with some sensors realted to the turbo pressure and have figured out that when the boost pressure valve (Please reffer to the pictures attached. Pic 1 Pic 2 Pic 3) is unplugged, the fault P0045 shows up but only when the two pipes leading up to it are unplugged as well. If the sensor is plugged in and the pipes are not, the code comes back up. I did check the pipes that are coming out of this sensor and they are both intact which lead me to believe that maybe the sensor is fauly. I have orrdered a new one and am waiting for it to arrive. If anyone has experienced something similar or have replaced this sensor, please drop a message.

Thank you.

Thanks for update. Found out erWin can no longer be accessed by paying public. Purely trade now.

P0045 usually points to the turbo actuator/control circuit, not soot. The motorway run rules out a stuck vane/DPF issue. I’d check wiring/connectors to the actuator first—heat can cause intermittent opens. That Pierburg valve could be it, but confirm with live data before replacing parts.

The pictures were showing the boost pressure valve and the part number for that is 059 906 629D. I have checked all the visible cables and they seem to be all good. What would the live data be called related to the boost pressure valve? I am currently using a scan tool called Kingbolen K7?

Thanks

I had this same code and it was my brake booster leaking vacuum. Get a smoke test done or buy a tester yourself..they are cheap.

Had a mate with the same issue and his actuator for the egr cooler was leaking vaslc when I tested it.

Update:

I have replaced the boost pressure valve from the same Audi A4 B9 2.0 TDI. I have done a test drive for about ah hour and the fault has not appeared yet which leads me to believe that the issue has been fixed.

Thank you to all that helped.

The boost solenoid below the egr one.

On the B9 it's located right on top of the engine. As soon as you take off the engine cover, it's on the right side of the engine, strapped to a metal bracket with a rubber belt thing. It's the boost pressure valve part number: 059 906 629D.

Yup that's the same part...that on the b8 model is down low on the front of the engine with the egr solenoid above it...the two of them fail a lot causing over boost alarms and boost actuator position alarm, that's why I bought my own smoke machine so I can test the system myself.