How to Replace the Temperature Coolant Sensor for a 2005 Trailblazer

by Justin Cupler

The TrailBlazer name originated as a trim level for the Blazer, in 1999. In 2002, the TrailBlazer became its own model, replacing all four-door Blazers, while two-door models kept the Blazer name. The 2005 TrailBlazer -- the last year before it replaced the Blazer altogether -- had a 4.2-liter six-cylinder engine as standard and 5.3-liter V-8 engine as an available option. Replacing the coolant temperature sensor on either engine is a similar process, with exception of the coolant refill procedure.

Step 1

Open the TrailBlazer's hood, and remove the radiator cap. Raise the front of the SUV, using a floor jack, and position jack stands under its frame rails. Lower the vehicle onto the jack stands.

Step 2

Crawl beneath the vehicle and find the lower radiator hose. Place a drain pan under where the lower radiator hose connects to the radiator. Squeeze the ears on the lower hose-to-radiator hose clamp with slip-joint pliers, and slide the hose clamp about 6 inches toward the engine.

Step 3

Pull the lower radiator hose from the radiator carefully, and allow all of the coolant to drain from the radiator and the lower radiator hose -- be prepared; the coolant will flow out of the hose and radiator quickly.

Step 4

Press the lower hose back onto the radiator once all of the coolant has stopped draining into the pan. Use slip-joint pliers to move the hose clamp to about 1 inch from the end of the radiator hose.

Step 5

Raise the TrailBlazer off the jack stands, using a floor jack, and remove the jack stands. Lower the SUV to the ground.

Step 6

Find the coolant temperature sensor on the front of the engine block, just behind the alternator. Pull upward on the locking tab on the coolant temperature sensor's wiring harness, and pull the wiring harness from the sensor.

Step 7

Loosen the sensor, using a ratchet, 6-inch extension and a 12-point socket. Remove the sensor the rest of the way by hand.

Step 8

Apply a thin coat of thread sealer to the threads on the new coolant temperature sensor. Allow the sealer to cure for the time specified by its instructions.

Step 9

Hand-tighten the new coolant temperature sensor into the engine and tighten it to 15 foot-pounds, using a torque wrench, 6-inch extension and 12-point socket. Plug the wiring harness into the receptacle on the new sensor.

Step 10

Add 50-50 premixed Dex-Cool coolant into the radiator until it reaches the base of the radiator's filler neck. Open the coolant reservoir and add 50-50 premixed Dex-Cool coolant to it until the coolant level remains steady at the "Full Cold" mark on the reservoir.

Step 11

Tighten the coolant reservoir cap and the radiator cap. Start the TrailBlazer's 4.2-liter engine and hold the engine's idle at 2,000 to 2,500 rpm until the temperature gauge reads about halfway. Allow it to idle for about three minutes, then shut the engine off. Allow the engine to cool until it is cold to the touch and check the coolant level in the coolant reservoir. Add 50-50 premixed coolant until the level reaches "Full Cold" on the reservoir. On the 5.3-liter V-8 engine, start the engine and hold at 3,000 rpm for 30 seconds, then allow the engine to idle for 30 seconds -- repeat this cycle until the temperature gauge reads about halfway. Allow the engine to idle for about three minutes, then shut the engine off. Allow the engine to set until it is cool to the touch and verify the coolant level is within the "Full Cold" range on the reservoir. Add more 50-50 premixed Dex-Cool coolant as needed. The regular-length TrailBlazer with a 4.2-liter engine has a 2.7-gallon coolant capacity, and the extended-length version has 3.45-gallon coolant capacity. The regular-length TrailBlazer with a 5.3-liter has a 3.05-gallon coolant capacity, and the extended-length has a 3.82-gallon capacity.

Take the old coolant to a used automotive fluid recycling center for disposal. Some auto parts stores take old coolant free of charge.

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