P0234 FAULT

[John1292]

Hi All,

I hope is the correct place to post this. I recently had an issue with my car, it is a 2016 XJ 3.0 D. (296bhp).

The engine management light had came on just out the blue and this had been going on and off for a few months. Most of the time I needed to clear it manually with a basic scanner as I had the rear if the EGR's clogging. I found that it was a P0234 Turbo/supercharger overboost.

After much brain storming and trial by error like cleaning out the throttle body, MAF sensor and temp sensor it was still not right. The engine did not go into limp mode at any time so was puzzling me even more. 

I thought of the worst case scenario to the fact it might be a turbo. So I disconnected the air flow to the main turbo on tick over, this was OK. I done the same to the secondary turbo and found there was no suction whatsoever. Initially I thought this was a problem. I started reading up and got a hold of a snap on diagnostic tool, went for a drive with the graph showing turbo boost. This is where I found that the secondary turbo doesn't work until hard acceleration or RPMabove 2800. Started looking around to see what fed the secondary turbo and found a valve unit with a vacuum unit attached situated at the bottom front drivers side behind the radiator. I disconnected the vacuum line, attached a pump to the vacuum unit and found it to be snapping open and shut. This was sticking quite badly. All I done was remove the whole unit. (Compressor/turbo shut off valve) and gave it a good clean with carb cleaner. Got the vacuum unit working smoothly and taken off the what I think is the recirculation valve of and cleaned the internals. Put back together went out for a test drive and all seems good. Now I can feel the secondary turbo coming in. What a difference. Hope this helps someone out there. I will attach a picture of the valve on a separate reply as I can't find the file at the moment. Thanks.