got an 07 roomster with 145k miles, had a few problems with engine power dropping and going into limp home mode, i replaced the MAF sensor the other week, this has improved things a bit as i did not get a CEL light until the other day

just took the car to local garage and checked the fault codes, got 17964/P1556 - Charge Pressure Control: Negative Deviation - intermittent

had a search,

found it can be

Boost Pressure too Low

Hoses/Pipes incorrect connected, disconnected or leaking

Charger Pressure Control defective

VNT (variable nozzle turbo): nozzles stuck

Solenoid Valve for Boost Pressure Control (N75) defective

i can check the hoses so my question is , how, what and where do i check the other possible cause,

just waiting for the car to cool down before i start checking thing, never had to play with the turbo section before so this bit is new to me

Edited 16 April, 201115 yr by bluecar1

fixed it

it was a pipe from the black valve unit infront of the windscreen on the drivers side

i broke a pipe on there 18months ago, and the bodge it and scarper repair i did to get the car on the road failed DOH!!!

i had the new set of pipes so put them on (i have to admit to having them for over 6 months but it looked a pain in the rear job so have been putting it off),

I immediately saw the problem as soon as i got the old pipes off, seems i have been driving and SDI roomster around for a good few months feeling the difference in performance, now got to wait and see if i get any difference in the economy which has been gradually decreasing over the last 6-8 months

Glad you discovered the fault and were able to fix it. It a normal diagnostic process you would probably go for the easy/cheap options first and work your way up to the expensive stuff. Problems with computer screens always start with is it turned on and is the brightness turned up