I have an '07 Chevy Malibu, whose turn signal doesn't seem to disengage whenever I make a turn, unless it's more than roughly 160 degrees (a U-turn). What are some of the possible causes and are there any easy solutions, as this is quite annoying to both me and the drivers behind when I forget to manually turn it off?
I don't know that car specifically, but it sounds like the auto-cancel mechanism is bent or mis-installed. Since it is integral with the steering column, you will probably need to pull off your steering wheel and get into where the switch mates with the column. There will be a plate or ring on the column with a tab or the like that will move a lever in the indicator switch when the wheel is turned.
I've seen this ring installed upside down in an old Porsche with an aftermarket steering wheel. The indicator wouldn't cancel because the tab was in the wrong place. Turned the ring over, put it all back together and it's fine.
This happens to me as well in my '06 HHR. For me, it's really just only when doing a small right turn I think. Lefts seem to go ok. When I was getting a heater core replacement, the mechanic that did it forgot to plug in a part of the airbag system, so I took it back, after which the turn signal would never turn off automatically no matter how I turned. After I took it back the second time, it was back to its old way (darn) so it may be a little more complex than just looking at the mechanism.
My point is, if it's getting pretty bad for you, you'll want to take it into a mechanic. For my particular car, they need to do a lot to get at the steering column.
When you're completing a turn though, try sticking your hand out towards the turn signal stick. I've gotten in to that habit so my hand catches the stick as I straighten out my steering wheel.