guys, I have a 2011 4,4 tdv8 with the typical very common 'restricted performance' (red) issue when second turbo kicks in, at 50mph, it flashes up'RP' in red. I get same codes each time.

P004C-77 -turbo supercharger boost control solenoid B cut low-mech failure commanded position not reachable.

and P004B-71 turbo supercharger boost control solenoid Bcct range/performance actuator is stuck.


I've read a lot on here, and have dismissed the following. -already changed out the CSOV changeover valve for a known good one. (I have a spare car to plunder parts. to fault the issue.) checked the operating pipe is securely cable tied on.
so now I'm reading on here, about the second turbo perhaps not operating, as per codes... I've read up on the arm seized/stuck, but just cannot work out how to attack this issue. I read up on the plastic bucket handle hook method, but can't for the life of me find a way in to get at it. I wonder if I have this issue, as I've read here that being under the car, and having someone turn on the ignition, you should hear both turbos 'cycle' the operation. I'm not hearing anything from second, but clearly hear the 1st, and hear 1st one cycle again when turned of... leave it a few mins, and try again and the 1st one, but never the second. I can get to the electrical plug, and have checked that's clean and plugged ok. is that the part that cycles, electrically? or is is through vacuum, and the actuating rod. -which might be jammed. I've got a pice of tin plate off to see further, from under the diff, looking up.
so, just wanting to know how to attack this proof of operation, and hopefully get the thing drivable again. no other codes/issues. ca can be driven with RP all ok, but limited throttle etc.

Last edited by johnboyairey on 25th Mar 2024 1:42pm. Edited 1 time in total

I thought the main turbo only has variable pitched blades that does the self test movement. Unless anyone knows better.

Maybe I should get under the other l322 (that’s currently fine) and compare the noises/observations.

As Kevinp says,the primary turbo on the right hand side only has a variable vane mechanism, which can be tested by cycling the ignition on and off. The left hand turbo is fitted with I think what is called a turbine shut off valve. This is vacuum operated, and directs exhaust gasses to the turbo when required,

SOLVED!
firstly with reference to finding the actuator arm on secondary turbo... I was reading that idea from a 3.6 engined three, so I totally went about the problem, with some bad info.
my issue was second turbo on my 4.4 wasn't kicking in, and giving the codes above. so, after checking various vacuum piping diagrams. (on here!). I saw that the second turbo actuator pipe is very long. when I checked its route, it goes from the vacuum pump, across the front of engine, and a black nylon pipe along the cylinder head right past tops of injectors..on the passenger side, and then changes to a more heat protected silver metal pipe vertically, towards the actuator. that coupling was uncoupled. no doubt by myself.
previous to this, I have changed out a broken (split) rocker cover on that side, which was split along the top due to brittleness, and was the obvious issue I first had when I bought the car. (bought with known issue) So, It was a bit disappointing to get a similar issue, after all the hard work I did. and its very tight down there. you have to get the engine mount bolt out, and jack up engine an inch to get the rear injector out. and all that wrestling must have caused the uncoupling. I recoupled the open pipes, and all is well. throwing no codes now, driving like a dream.

Very satisfying.

johnboyairey wrote:

SOLVED!
so, after checking various vacuum piping diagrams. (on here!)

Sounds a bit like the YT of LRTime when he got his new405 "The Queen "

He spent days trying to get to the bottom of the problem
His face is priceless when he realised what was causing it
Oh my God