1.6hdiTurbo Over Boost OBD code P0234

[JohnM]

My lovely 2007 1.6hdi Berlingo has thrown a new fault to keep me amused! I've got P0234, engine light and limp home mode which occurs under acceleration or at motorway speeds. This code relates to turbo over boost.
I have recently replaced the head gasket so my first thought was what have I messed up.
So far I have;
Checked all inlet hoses for leaks.
Replaced pressure sensor on the throttle body (DOSER).
Checked vacuum hose for damage and connections.
What I do know is that I have a constant vacuum at the pipe where it enters the turbo actuator on tickover.
The wastegate/variable vane lever moves fully towards the vacuum unit on tick over and returns to the no-vacuum position on switch off.
Can any one confirm that the turbo should be in this position on tick over or give me any other ideas?
The suspect appears to be the electrical vacuum servo at the back of the engine, (Why have they buried it there?) but the fact that I have recently had the engine apart makes me wonder if I have cocked something up. Any thoughts?

[JohnM]

I have now established that vacuum = boost, no vacuum = no boost.
I have also found that if I switch off after a run the vacuum remains in the actuator, the wastegate/variable vane lever only returns to the rest position if I pull the vacuum pipe off the vacuum unit.
Can anyone confirm if this is normal?

[JohnM]

I've replaced the electrical vacuum servo at the back of the engine, caned the nuts off it around a few country lanes, no sign of the fault returning, fingers firmly crossed.

As an aside, I have run numerous knackered old sheds over the years and I can say that none have been so absolutely unreliable as this Berlingo. The thing is literally falling apart, over the last 12 months I have replaced the crank sensor, the DOSER, the EGR valve, the electrical vacuum servo at the back of the engine, the cylinder head gasket, it appears to have snapped a cam-belt a couple of years ago and on top of this it's a rebuilt write off. I'm thinking of renaming it Lucky!

[JohnM]

Fault came back on one occasion today, but not as bad as before, how I hate this van!

[Noel Brig]

what sort of mileage has it done ?

[JohnM]

what sort of mileage has it done ?

It's done just over 80,000 miles, which appears to be genuine. The internals are all clean which support this as do previous MOTs.

I can't help thinking it's something I've done whilst changing the head gasket, but I'm at a loss as to what. The fault developed immediately after having the engine apart which makes me think this.

Prior to the work the inlet manifold may have been leaking at the head, but I used new "O" ring seals when I replaced the manifold and there are no obvious leaks.

The only other thing I have changed is that the EGR was blocked off, but I put it back to standard when I put it back together.

Any suggestions would be gratefully received. :brickwall:

[Noel Brig]

Firstly I know very little about ECUs BSIs and modern hi tech diesel engines, so the following is just a wild thought; When the EGR was originally blocked off, could the ECU have been re-mapped to account for this, now with the EGR unblocked, could the ECU be getting confused.

Curious - what had caused the head gasket to fail ?

[JohnM]

The head has been off previously as it has clearly snapped a cambelt a couple of years ago and it was accident damaged when I got it, rad split. So it may have been badly reassembled after the cambelt or perhaps boiled up after the accident.
It has had a minor coolant loss for the last 12 months, but the gasket let go properly a few weeks ago.

As for the EGR I blanked it off so no re-map.

[JohnM]

Just an update for anyone with the P0234 code and limp home mode, I had the fault re-occur after I had done some under bonnet work around the rear of the engine. All I did was remove an EGR blanking plate and TIDY UP THE VACUUM PIPES to the turbo servo.
To cut a long story short there are three pipes that go to this unit (at the back of the engine block) one is from the vacuum pump, one is to the variable vane actuator on the side of the turbo and the third exits to the atmosphere via a very small filter on the top of the engine.
What happens is that vacuum to the turbo causes maximum boost and when the actuator tries to reduce boost it switches the vacuum to the atmosphere via this third pipe. If this pipe is blocked then the vacuum remains and the turbo over-boosts.
All three pipes enter the servo unit via the bottom of the unit and as a result there is a rubber "U" at the end of each vacuum pipe as it loops round to the unit.
What I think has happened with my van is that the pipe leading to the top of the engine (atmosphere) has been routed incorrectly and when I have tidied it up it has folded up around this "U" and blocked the pipe. This in turn has prevented the servo from dumping the vacuum (if that's the correct term) and the turbo remains on full boost.
I cured this problem temporarily by reaching down the back of the engine and pulling the atmosphere pipe (the one nearest the centre of the vehicle) from the actuator allowing it to vent properly.

IN CONCLUSION IF YOU HAVE A P0234 FAULT CODE THEN THE VACUUM ACTUATOR UNIT AT THE BACK OF THE ENGINE IS THE PRIME SUSPECT, BUT IF YOU MAY HAVE DISTURBED THE VACUUM PIPES THEN MAKE SURE THE PIPE THAT LEADS TO THE TOP OF THE ENGINE IS CLEAR.

[ron]

Glad you managed to fix it.:thumbsup::woop: