Hi my name is Hal.
Do all bulbs work front and rear, on the left side? When the turn signal flashes fast, it is usually just a burned out bulb. Inspect all bulbs,on left side for turn signals.
Are the left side lights lighting up the same number of bulbs as the right side? If so then the body control module is not sending the signal for left turn to one of the lamps. Which lamp is inop when left turn is on . Front or Rear?
Here is the description of how the turn signals are operated on a cobalt.
Diagnostics with a scan tool may be needed to determine the fault with the body control module. Diagnostic codes may be set and will not illuminate a fault warning lamp.
Turn Signal Lamps
The body control module (BCM) is responsible for controlling the turn signals and hazard lamps. When the turn signal switch is placed in either the left turn or right turn position, the BCM receives a signal from the turn signal switch. The BCM then sends an on-off voltage signal to either the left or right turn signals and their instrument panel cluster (IPC) indicator. When the hazard switch is pressed, the BCM receives a signal from the hazard switch. The BCM then will send an on-off voltage signal to all the turn signal lamps. All the turn signal lamps will flash including both IPC turn signal indicators.
The body control module (BCM) is responsible for controlling the stop lamps. When the driver presses the brake pedal, the BCM will receive a signal from the brake pedal position sensor. The BCM then supplies battery positive voltage to both left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL).
Short to Ground
Short to Voltage
Hazard Switch Signal
Left Turn Signal Switch Signal
Right Turn Signal Switch Signal
Turn Signal Lamp - LF Control
Turn Signal Lamp - RF Control
Stop/Tail/Turn Signal Lamp - LR Control
Stop/Tail/Turn Signal Lamp - RR Control
Hazard Switch Ground
Stop/Tail/Turn Signal Lamp - LR Ground
Stop/Tail/Turn Signal Lamp - RR Ground
Turn Signal/Multifunction Switch Ground
Turn Signal Lamp - LF Ground
Turn Signal Lamp - RF Ground
1. Turn Signal Lamps and/or Indicators Malfunction
2. Hazard Lamps Malfunction