The Cobalt arrived in the 2005 model year alongside its predecessor, the Cavalier. In 2006, Chevrolet decided to end the Cavalier's production life and replace it with the Cobalt. The 2007 Cobalt had three different engines available: The base engine was a 2.2-liter, four-cylinder that created 148 horsepower; the next option was a 2.4-liter four-cylinder that produced 173 horsepower -- this engine only came in the "SS" trim level; the highest engine level, which only came in the SS supercharged model, was a 2.0-liter, supercharged four-cylinder that made 205 horsepower. The coupe and sedan Cobalts had different taillight styles. The coupe had a circular taillight design, like the Corvette, and the sedan had a large, teardrop-style taillight. These two taillight designs have different, but similar, taillight replacement processes.
Open the trunk and remove the clip holding the carpeting behind the taillight assembly. Pull the carpeting away from the taillight assembly, exposing the rear of the taillight assembly.
Pull up on the locking tab on the harness connecting to the taillight socket, then pull the harness from the socket.
Grab the rear of the taillight socket and turn it counterclockwise to unlock it, then pull it from the taillight assembly.
Pull the old taillight bulb from the taillight socket with a slight wiggling motion.
Grab a new 4157 taillight bulb with a clean, lint-free cloth and press it into the socket. Insert the socket and the new taillight bulb into the rear of the taillight assembly and turn it clockwise to lock it into place.
Plug the wiring harness back into the rear of the taillight socket. Set the trunk carpeting back over the rear of the taillight assembly and press the clip until it secures the carpeting in place.
Close the Cobalt's trunk.
Open the Cobalt's trunk and remove the trim clip holding the carpet directly behind the taillight lens, using a trim stick. Pull the carpet from behind the taillight assembly, exposing the back of taillight assembly.
Remove the two thumb screws from the inside part of the taillight assembly, then pull the taillight assembly from the Cobalt.
Turn the taillight assembly over and remove the taillight socket -- the socket at the center of the taillight assembly -- by twisting it counterclockwise and pulling it from the taillight assembly.
Grab the old bulb and pull it from the socket with a slight wiggling motion.
Grab the new 4157 taillight bulb with a clean, lint-free cloth and press it into the taillight socket.
Insert the socket and new bulb back into the rear of the taillight assembly and turn it clockwise to lock it into place.
Set the taillight assembly back in place on the rear of the Cobalt and tighten the thumb screws to secure it.
Reinstall the carpeting over the rear of the taillight assembly and press the clip in place the secure the carpeting.
Close the Cobalt's trunk.
