Problems with Av/Tv-mode, underexposure, help!

[nira]

Hi, I hope someone has some good advice to a problem i have with my camera, a Canon EOS 400D/XTi. When in Av-mode or Tv-mode, the camera sets the aperture and shutter speed to an underexposure of -2, each time. When I set the aperture i Av-mode, the camera sets the shutter speed to way too fast, and if I set a shutter speed in Tv-mode the camera sets the aperture too wide and the result is all very dark pictures. However, in fully manual mode, M-mode, the light meter shows the right exposure, so i can set the aperture and shutter speed right and get the right exposure. But in P-mode, Av-mode and Tv-mode, when the camera automatically sets the aperture, shutter speed or both, it is always at an exposure of -2.
I've tried with a couple of different lenses, so the problem is the camera.
So I'm wondering if anyone has had the same experience or if anyone knows what is causing this, and if it can be fixed.
Thank you in advance! : )

[TPF Sponsor]

[Overread]

You have set your exposure compensation to underexpose the shots in Av/Tv modes - check your camera manual for exposure compensation in these modes to turn it off. Its a good feature and is needed sometimes, but as you have found out its not something you want on all the time.

[musicaleCA]

Wide aperture = more light. Smaller aperture = less light. (I know; f-stop numbers are more than a little confusing, going up when the amount of light is going down.)