All Chevy Trailblazers are equipped with automatic transmissions, which use filters to clean the impurities in the the transmission fluid. You need to change your car's transmission filter at the same time that you change the transmission fluid; for the 03 model, you need to do this job every 30,000 miles or 30 months. The transmission fluid pan on the Trailblazer is more or less centered on the undercarriage, making it slightly difficult to reach.
Raise the car with the jack and support it on four jack stands. Place a drain pan underneath the transmission fluid pan and check to see if the pan has a drain plug.
Disconnect the shift linkage that runs along the driver's side of the transmission pan--disconnect the cable end from the ball stud and then remove the bolts that mount the cable bracket to the transmission--this is needed to access some of the transmission pan bolts.
Unscrew and remove the drain plug, using a flare-nut wrench, and let the fluid drain into the drain pan.
Remove the mounting bolts for the transmission pan, using the wrench, then carefully pry off the pan with a flat-head screwdriver. If the pan doesn't have a drain plug, remove all but the corner bolts and then slowly remove the front bolts, so that the fluid drains into the drain pan.
Pull the transmission filter straight down to remove it from the valve body inside the transmission.
Clean off all traces of gasket sealant from both the transmission and pan, using solvent and a rag. Dry the surfaces with compressed air.
Install the new filter in the transmission with a new seal; the seal is often pre-installed on most replacement filters.
Attach a new gasket onto the flange of the transmission pan, and then install the pan back on the transmission with its bolts. Tighten each bolt a little bit at a time, working around the pan's circumference.
Reconnect the shift linkage, using its bolts, and connect the cable end to the ball stud.
Lower the vehicle off the jack stands.
Fill the transmission with four quarts of Dexron III automatic transmission fluid through the filler tube at the right rear end of the engine compartment. Use a funnel to aid in pouring the fluid.
