There are many problems that come with owning a car. If a Left rear brake and turn signal do not work, a person should check the fuses, bulbs and wiring.
Bulb is out.
Start with checking the left rear brake light bulb.
The turn signal and brake light use the same bulb. When you get a fast flash, it is from a reduced electrical load being placed on the flasher unit due to a burned bulb. Replace the bulb and this should fix your problem.
Could be a loose ground for the left rear light socket.
Usually when ones turn signal is blinking fast its telling you that a turn signal bulb (and in some cases a brake light bulb) is out. If it blinks fast when you turn on the the left signal the burnt out bulb is on that side of the vehicle (could be front or rear bulb so you'll have to check). And vice versa
More than likely you have a burnt out bulb at the front signal light, rear signal light, or brake light on the right side.
Where is the left rear brake and turn signal relay located on a 2010 Chevy express van. V-6
Check the ground wire and the light socket for the left turn signal bulbs (front and rear). You might be getting a ground loop.
Normally this is caused by a weak ground at the left turn signal bulb.
If only the right rear brake/signal light is effected it is not the fuse. Inspect the right rear brake/signal bulb, socket and wiring.
you have a blown bulb, some vehicles use a double filiment bulb that operates the turn signal and brake light
the turn signal switch is probably bad