I first noticed this issue a little while ago when my car went into limp mode on the motorway. When connected to my OBD reader, it gave the error code P0299 which means the turbocharger isn’t producing the expected pressure values. After some research, I found that this is a common issue with VNT turbochargers and is usually down to a faulty turbocharger actuator. I found the correct part online and ordered it to arrive the following day.
Upon removal of the OEM turbocharger, it was clear it wasn’t going to be as easy as I’d hoped – the clearance between the bottom of the actuator thread and the exhaust manifold was barely enough to get a socket on in order to remove the locking nut that held the vane arm in place.
After a fair bit of struggling, I managed to get it on and removed the bottom lock nut which allowed me to lift the faulty actuator from the turbo. I did want to test this though before installing the new one as I still didn’t 100% know if it was in fact the actuator that was the culprit so I used a vacuum pump and connected the hose to the N75 valve on the actuator to simulate the pressure it would usually need to cause the actuator arm to extend.
As I expected, there was a clear vacuum leak within the actuator diaphragm. The actuator arm extended ever so slightly and returned to it’s resting positing which was further reinforced by the reading on the vacuum pump showing it wasn’t holding pressure.
I now had the new actuator to fit but first I hooked it up to the vacuum pump and checked it was working as intended. Once this was confirmed, I then simulated full pressure to the actuator in order to insert the upper lock nut (along with some threadlock) to ensure the VNT arm would be locked in the correct place when installing it back on the turbocharger.
Installing it back on the car was equally as tricky but in the end I got the lower locking nut on the arm. As soon as I pulled away to test the actuator, I could instantly tell my boost was back and my car had the power it had before the actuator failed!
