2005 S40 boost pressure sensor P0236 code
 

2005 S40 T5 2.5l turbo - where is the boost pressure sensor located?
Intermittent sluggishness, turbo not working properly 155k miles (P0236 code).

I believe the T5 uses the MAP sensor for this function. I believe this is the location for your car:
https://cimg1.ibsrv.net/gimg/volvofo...438ab98afb.jpg


Might be worthwhile to get a USB Bluetooth "dongle" and put the Torque Pro app on your phone (if you have a 'droid phone) - about $25 all-up, and you'll be able to monitor the actual vacuum / boost, as well as a LOT of other useful things. There are host of things that can cause this kind of problem - plumbing "leaks" in the turbo system (my V70 T5 ran horrible when the cross-over pipe came loose, for example), or of course, a worn-out turbo (not at all unusual with the kind of miles yours has).

The bluetooth thing sounds like a great idea. I saw a few of these looking them up. Is there a specific one you can recommend?
I do have a code reader, but you can't exactly drive around with those plugged in so easily.
Edited. I have identified correctly the part that is the problem but this pic is wrong. Part should be Bosch #0 261 230 090
https://cimg6.ibsrv.net/gimg/volvofo...283d5d4354.png

The best dongle depends on the phone you use. The one I've had good luck with is the Foseal OBD adapter (it's blue, and about $10 from Amazon, for example).

There's a free Torque Light app, but the full-featured Torque Pro app is only $5 or 10... best deal you'll ever get on diagnostic stuff for your car.

If you need to validate which parts fit, you could check out the excellent rockauto.com website - even when I need to buy elsewhere, it's a HUGE help being able to look up the right part numbers, many which have extra info when you "drill down". Of course, I buy a LOT of parts from rockauto, since their pricing is as good as anyone out there and usually better.

I will look into those, definitely want something like that. I have a Samsung Note 3.

Update:
Found MAP sensor behind passenger side strut. Checked for continuity, had 22 ohms. Found TURBO BOOST PRESSURE SENSOR mounted to intercooler behind the passenger side fog light cover. Plug had water in it and connections were corroded. Replaced the part, sprayed some contact cleaner in the plug. re-seated silicone seal in plug (it was not properly in place hence the water). To get to it properly IO had to remove the front bumper skin. You can almost access it from the fog light cover but not quite.
Put everything back together and it is good to go. I may need a new turbo unit but I don't need it today.

Habby thank you for your help and advice.

This is where it was. On top of the pass. side of the intercooler.