Engine BKD 2.0 TDI 16V 

OK. First I will tell you the problem. Probable overboost followed by limp home. As with windows, shut down start-up works again.

Someone said it might be the MAF sensor, unplugged it and engine warning light on. No turbo AT ALL!

Plugged it back in. Warning vanishes, but no turbo whatsoever. Tried my rubbish Chinese OBD2 to clear codes, but it's garbage.

Gives me an error. 

Waiting for RAC man to rescue situation or give my turbo the last rights.

My questions are as follows.

EGR valve 

There appears to be a EGR valve(refered to as mechanical EGR valve?) at the FRONT next to the inlet manifold.

Everyone insists that it's at the back where there is a "radiator flap for EGR". Is this the EGR or just a part of it?

How do the two work together?

EGR, as far as I can tell is about reducing the nastier nitrous compounds by feeding directly from the exhaust manifold "oxygen free" gas, which lowers the combustion temperature. 

What happens when the engine goes into limp home after a bad overboost(say through stuck turbo vanes) is this EGR valve/valves involved in basically disabling the turbo or is there another system involved?

 

 

 

 

 

There are a few posts on here with similar issues, including some by myself although I have the BKC engine.

 

Before condemning the turbo at great cost, ensure the mechanism moves freely from stop to stop, either pneumatically or electrically with a positive return.

 

Then check vacuum and any electrical connectors/sensors.

 

It could be simply a cracked vacuum hose, bad sensor, worn out actuator or sticky VNT mechanism.

 

All cheap to fix.

Thanks MicMac. Unfortunately I  must admit my own sins(No body expects the Spanish......) Yep, the actuator vacuum pipe came off after some shoddy workmanship.

Make sure you push the spring clip right over the join not 1cm down the pipe or elsewhere.

But my other questions as to how the EGR valve(s) work together and how the engine disables the turbo after bad overboost is what I would love to know.

The 1.9 engines have a rear mounted EGR, the 2.0 are front mounted AFAIK...

 

You are correct re EGR purpose.

 

Once the ECU detects a turbo overboost condition it electronically stops the vacuum to the turbo actuator via the vacuum solenoid block/controller, leaving the turbo in the LOW boost position.

 

I can't imagine the EGR would operate any differently or have any bearing on the matter.

Thank you for your patience and your time!!!!! I value it. This is my last query!!!

Excellent! That does help. But what happens if stuck on full. I imagine that doesn't happen often, but what is the safeguard?

I have sort of got to the bottom of the radiator flap for exhaust gas recirculation, at the BACK of the engine. This seems to be a variable control of the exhaust flow to the small radiator then to the EGR pipe and finally EGR. What's confusing is that some call this "Radiator flap for EGR"  THE EGR valve! I suppose in a very real sense it is and gives more control than THE EGR valve at the front of the engine which is a pressure controlled EGR on/off valve!!

Is this correct

 

 

The turbo is mechanically failsafe to the LOW boost position unless it is jammed.

 

I think you are referring to the EGR cooler where the exhaust gas is cooled before being added to the intake air stream.