AE problem with 420ex flash

I encountered a problem when attempting to use an external flash (420ex) in P mode. There was a fair amount of indoor light (indoor swimming pool) and I was using the flash as a fill-in and to increase the shutter speed. Unfortunately, it would appear that the camera would not factor-in the flash and every shot would get over-exposed. AE would result in target exposures of 1/15 sec. at f2.0 which would produce almost a completely white picture. To avoid the over-exposure I switch to Tv mode and increased the shutter speed to 1/250 sec which ended up with an underexposed picture. Does anyone have any idea why the camera would not get a proper exposure in P mode with the external flash?

I do not usually have this problem when shooting low-light indoor pictures with the flash. Is it possible the camera was basing the exposure purely on the flash and distance and not factoring in the ambient light?

Check the EXIF on the overexposed pictures. What does it say under flash? It should be something like "External E-TTL". It may be that the G2 isn't properly recognizing the 420EX. There have been some occurrances of this reported in the dpreview.com Canon forum.

If this is the case make sure the 420EX is properly pushed in all the way and the locking ring turned.

If all else fails you may have a faulty 420EX. You should not be getting overexposed pictures in P mode.

I'll second that about checking that the flash is sitting in the shoe properly.

Just received my 420EX today, and it would't fire until I re-postioned the flash once or twice. The third time I took it off and put it back on (at which time it 'felt' more like it went on properly), it worked no problem.

Just had to get the feel for it I guess.

Tom