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Thread: P0234 -5B Fault

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    Default P0234 -5B Fault

    Got this code on my car.

    P0234 - Boost Pressure Control Circuit Positive Deviation
    (5B) - Present

    It happens when I do 3600 RPM in 3rd gear, rebooting the car turns the EML off and takes it out of limp mode. I have had a good look at all the hoses and the only one which I could see that was damaged was a small vac hose at the front of the engine, which I have replaced.

    I have had the EGR off the car and cleaned it all out, including the soliniod even cleaned out all the gunk in the butterly as it was covered, the manifold looks very sooted up.

    I think I will have to admit defeat and take it down the garage and get them to pressure check all the pipes/hoses, done a bit of research and it seems to point towards a split hose etc, well I hope that's what it is.

    What ya reckon?

    Frenchman

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    Full Member bobssignum's Avatar
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    Boost sensor needs a clean , or you have a hole or split in one of your hoses.
    Driving vauxhall,s for 30 + years
    and still loving it

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    I did clean the boost sensor at the same time I removed the EGR. It was very sooty, I also cleaned the hole where it cam out of as best I could.

    I am wondering if I can measure the resistance to determine if it's actually faulty, does anyone know what it should read when switched off?

    Frenchman

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    Regular Member mattv6diesel's Avatar
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    negative deviation is a over boost code could be the boost actuator valve sticking or the boost sensor has just failed

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    So does positive deviation mean an under boost, like a leak etc? Are these boost valves a common problem to fail completely on these?

    I had this problem both before and after cleaning the boost valve, one odd thing is it doesn't seem to cut out if I do over 3600 rpm in 2nd gear, although it is possible that a little higher RPM in this gear would have the same effect.

    What is frustrating is I have a compressor at home but not a kit to pressure test the hoses

    Frenchman

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    Regular Member mattv6diesel's Avatar
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    yes it does. sure you didnt clean the egr valve? the boost valve is the vacume pack under the front slam pannel 2 are fitted side by side and are identical

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    I think I am getting a little confused (not difficult) I cleaned the sensor that lives in the manifold next to the EGR at the back of the engine. So this boost valve can it be cleaned out, or is is a straight swap?

    Will have a look in the haynes manual and see if there are some pics, on the front of the engine bay there is a little white devive that says vac out on it, and the pipe that went from this to a small metal pipe had split, this is the one I replaced.

    Frenchman

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    For anyone that's interested, I found the problem to be that the vanes were stuck open on the turbo causing an overboost, and a lack of power in the low revs.

    I removed the turbo, separated it from the manifold and cleaned up all the crap in there that was keeping the vanes stuck in an open position, I then free'd up the siezed actuator wastegate by working it in and out by hand, I also removed a bit of rust with some sand paper.

    Car pulls pulls perfectely now

    Right pain to get the thing on and off the car, some very awkward bit's to get to, but alot cheaper than a new turbo

    Frenchman

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    thanks for responding with you fix, I have the same error code now.

    any thoughts on what to check before removing the turbo?

    boost pressure sensor in the manifold just cleaned, hoses seem ok

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    I would change the boost sensor first as it is easy and not too expensive, I tried this as a first resort before I tackled the turbo.

    I took my turbo off and seperated it to clean, fault was caused by a split hose that wasn't replaced by last owner and had allowed the turbo to get sooted up, the mechanisam that open and closes the finger vanes also had some rust and had siezed so even after replacing the hose the turbo still didn't work

    The car had no pull at all before I did this fix and now pulls from about 1500rpm, here are some photo's and a video. Quite a pain to get to the turbo, I removed the front bumber, radiator etc just to get access.















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