More then likely it needs to be replaced, if its the actual signal inside the car, turn it on check outside the car which one it is and replace!!
turn signal relay is bad
your rear bulb is blown - replace the bulb The turn signal blinks fast because the bulb is going out. That is also why the others dont blink.
Buy a "highway" turn signal flasher
Check your bulbs and your flasher.
Why would you want the blinker faster. They should blink at factory specs.
Probably needs a fuse.
This happened to me. When my turn signal lights went out or would stay solid where I would have to manually make them blink it eventually made my break lights go out, but they would come on when I held the turn signal switch for high beams. To repair the issue you will need to get the whole turn signal switch fixed which is behind the horn and the airbag. Nice penny and it takes about 2-2 1/2 hours to repair it because there are wires behind your steering wheel that go to different things.
You either have a bulb burnt out or the turn signal flasher is bad.
turn signal relay fuse
If the check engine light does not flash when in the diag mode, the problem is the computer. Could be as simple as a failed lamp driver but a failed computer is toast and will need to be replaced/