The engine management light is on in my l405 and i've been told it is the turbocharger boost control solenoid. As a result of this ,the vehicle goes in to restricted performance mode.I was wondering if anyone knows where this is located in the engine bay and how much it would cost to buy a boost control solenoid.

A solenoid is used to control the inlet isolation valve (also called a shut-off valve) for the secondary turbo. The current replacement part appears to be LR076025 and includes associated vacuum pipes and is expensive so you would need to be certain that the solenoid has failed. LR have a specific test to determine whether the solenoid or the valve is at fault.

The solenoid is in the area at the top front of the engine. A vacuum tube runs down in front of the engine to the valve which can be spotted looking down between the engine and the radiator off-centre towards the left side of the vehicle.

What operating conditions causes the fault? The secondary turbo is only used from around 2500 rpm.

If the solenoid is sticking then blowing compressed air through it may fix it. It is normally operated using a pulsed (PWM) signal but straight 12V can be used for short periods.

This now seems to be a known fault, my car had the same symptoms just inside warranty. Others have also had turbo problems. Try and get LR to pay. letters not necessarily in the right order

Assuming the valve is the same as on my L322, the build up of road grit/dirt and salt can cause the valve to stick and a good squirt of WD40 or similar penetrating oil can free it . They stick because they get called into use so infrequently, and also the very small amount of movement when it operates.
Mike. G reg 2.5VM Vogue Portofino red 1991- 1999
V reg 2.5td P38 Rioja red 1999- 2006
53 reg td6 Vogue Oslo blue 2006- 2015
11 reg 4.4 TdV8 Vogue SE. Baltic blue 2015- date.
https://www.fullfatrr.com/forum/topic56162...tty+affair

I wonder if the fault is the known problem of the engine in later vehicles where oil from the level sensor finds its way into the electronics of the primary turbo.