There are two oxygen sensors on a 2000 GMC Sonoma. One is located on the left (driver's side) of the Y-pipe up high near the manifold. The other is located on the exhaust pipe on the right (passenger's side) going to the catalytic converter. Figuring out which one is bad can be trickier than replacing them. However both the oxygen sensors in this model are exactly the same part number. You can buy a quality aftermarket sensor at a reputable parts store for about $60 each and save yourself labor charges by installing them yourself.
Park the GMC Sonoma on a flat paved or concrete surface and apply the parking brake.
Place a wheel chock behind one of the rear tires.
Lift the left front quarter of the truck with a floor jack and place a jack stand under the front left frame rail. Repeat this for the right side to elevate the front axle of the truck.
Put on the safety glasses. Grab the tools and new sensor. Crawl under the truck on a creeper if you have one.
Locate the sensor you need to replace. The upstream is on the left-hand side (driver's side) of the front exhaust Y-pipe near the manifold connection. The downstream sensor is near the catalytic converter.
Spray the threads of the sensor with the spray lubricant and allow it to soak in a little.
Unplug the wire harness from the sensor. Use the screwdriver to press in the locking clip on the plug and separate it. You may have to pry out the plastic push pin to make it easier, but you can use the screwdriver to do that, too.
Place the wire of the sensor through the hole of the 22 millimeter box end wrench and attempt to loosen the sensor turning it counterclockwise. A lot of times, the sensor will loosen when applying the proper amount of strength and tenacity. However, you may need to heat the pipe area where the sensor threads into with the hand torch to expand the metal around the sensor threads. If you have to do this allow it to cool down before reinserting the new sensor.
Apply a light coat of anti-seize lubricant to the threads of the new oxygen sensor. Be careful not to get any on the sensor head. Many quality sensors may very well already have some anti-seize lubricant coated lightly on the threads.
Screw the sensor into the pipe by hand at first and tighten with the wrench. You'll have to feed the wire of the sensor through the box end of the wrench again. Tighten securely, but realize there's only 4 or 5 threads on the sensor so over-tightening it can easily strip out the threads and damage the sensor.
Plug the wire back into the harness and the push pin back into the pre-drilled hole.
Collect all the tools and old sensor from under the truck and lower it down.
