P0234-05A Negative Deviation

[raxx]

Hi Chaps

I got a very intermittent P0234-05A on an Astra H Z17DTH.

Now that's negative deviation but after reading some threads I am a little confused as I keep reading stuff like this:

P0234-5b is positive deviation meaning boost pressure too low (underboost)
P0234-5a must be negative deviation meaning boost pressure too high (overboost)

Now I always thought 'Negative Deviation' meantion too little boost pressure is being detected at the boost pressure sensor to what is being 'commanded' and 'Positive Deviation' meaning the reverse, boost pressure detected too high at the sensor.

Or does this vary from make to make? ie I worked on a VAG 1.9Tdi PD lump some months ago where we were getting neg deviation and when I pluigged up to it and took the readings I could clearly see the detected pressure was way lower than the command pressure set hence 'Neg Deviation'

Or am I going bonkers?

[Deleted]

EDC 16 p0234 5a turbo load pressure too high.

EDC 16 P0234 5b turbo load pressure too low.

[raxx]

Hi Mac

OK, not sure why then it's called 'neg deviation' then logic would say thet 'neg' means below the command request hence lower pressure...

If the turbo pressure is too high I'll have to look at the actuator and solenoid to see if they are operating then I guess....

Thanks.

[Deleted]

Where did you get your trouble code description from ?

[raxx]

My description is from the daig tool op-com, pulled the code from the car and it was described as:

P0234-5A Boost Pressure Control Circuit Negative Deviation

Maybe I'm thinking the wrong thing as looking at that now it's describing the 'control circuit' rather than the 'actual boost pressure' at the map sensor.

[Deleted]

Over boost -

If the measured intake boost pressure is over the deviation upper limit then the high boost average calculation is positive , if the measured intake boost pressure is below the deviation upper limit then the high boost integration is negative , if the integrated value exceeds the maximum limit a fault code for high inlet pressure over boost is set ,

the reverse for under boost .

;D ;D

[raxx]

Cheers Mac

[Deleted]

There not that good at controling the inlet air buterfly when they begin clogging the inlet.