I have a '05 C230 with about 108K miles. I'm getting a P0238 code (Turbo/Super Charger Boost Sensor A Circuit High). It's probably a result of an error of mine since I just did some work on the car. Here's what I did (an attempted):
1. I replaced the serpentine belt - pretty straightforward. Of course I disconnected the air inlet silencer. I saw a little oil in the silencer when I disconnected the hose to it.
2. I noticed a bunch of grime on the front of the engine around my cam magnets (I have the pigtails). I took a connector off both magnets and there was oil in them. I sprayed some degreaser in the plugs and let it drip. I took the exhaust cam magnet off to look at it. Made a note to get a new set of cam magnets, o-rings, and grommets from rmeuropean, wiped the cam magnet cover off and bolted it back on the engine. Then sprayed some degreaser around the area and wiped it off.
3. I attempted to get to the MAF to clean it as I had never done that on this car. When I got to the part where you disconnect the duct from the MAF to where it goes down to those hose clamps, I chickened out. I still had the stock MB hose clamps and I couldn't even see it so I reconnected the big plugs on the right (looking from the front) of the air box, the booster hose, and screwed the back bolts of the air box back in.
4. I put supercharger oil in my supercharger. I did not notice that some of the oil leaked out. Maybe I didn't insert the tube I used to feed it oil deep enough into the SC because there was a little puddle of oil on the floor when I started putting everything back together.
5. checked my timing chain. I had a hard time getting the plastic cam cover loose and in the end was only able to lift it an inch or so because it was catching on the air box. I also didn't fully disconnect the wiring harness that crosses the cover from the right side toward the rear to the left side toward the front. I was able to see that my chain was tight and I screwed the cam cover back down.
6. I replaced the connector to the water reservoir near the engine because it snapped off.
7. I took off the duct on the air intake (throttle body?) next to the SC and cleaned the throat and butterfly in there as best I could with MAF cleaner.

I put everything back together. I have a sinking feeling that I missed connecting an electric plug but I have looked three times and don't see anything unplugged. I double checked all my other hose connections, etc.

I test drove it and it ran fine but seemed low on power (duh! - no SC!).

Any help, comments, advice, or suggestions would be greatly appreciated!

 

I found the problem! I read where somebody had a similar problem that was caused by a loose hose to the intercooler. I had monkeyed with the hard duct to the throttle body so I rechecked those connections. They were good. When looking for other intercooler hose connections that might be loose, I noticed the left hose (as looking from the front) to the intake air silencer was not completely clipped into the silencer. It, along with the hose on the other side of the silencer were disconnected to give room to change the serpentine belt. Surely an air leak going into the silencer wouldn't cause this! But it did. A test drive confirmed that it had the power it used to!