The Chevy Tahoe was introduced in 1995, and it is a relative to the Yukon--the GMC version of the SUV. The Tahoe basically replaced the full-sized Chevy Blazer. Available since 1996 with V8 engines, the Tahoe features four O2 sensors (also known as oxygen sensors). There are two of these sensors located in front of the catalytic converter, and they are designed to monitor the fuel and air ratio mixture in the exhaust. Two more sensors are located near each converter, and serve to monitor their efficiency. One or more of these sensors can become defective and will need replacement.
Locating the Faulty Sensor
When an oxygen sensor fails, the "Service Engine Soon" light will illuminate on the dash. Take your Tahoe to an auto parts store to get the on-board computer scanned. Auto parts stores will perform this service for free, and they can help you determine which sensor(s) have failed. Since there are four sensors on most Tahoes, the scanner will be able to detect which one by reading the "check engine" codes: Bank 1, sensor 1 is the upstream sensor on the cylinder 1 side of the exhaust system; bank 1, sensor 2 is the downstream sensor on the cylinder 1 side; bank 2 sensor 1 is the upstream sensor on the opposite side of cylinder 1; and bank 2, sensor 2 is the downstream sensor on the same side.
Purchase direct-fit sensor(s). Direct-fit sensors integrate the plug-in outlet, therefore no rewiring is required. These sensors cost slightly more than universal sensors. Also, universal sensors require eliminating the male and female plug counterparts from the wire harness. Direct-fit sensors, however, do not require any wire splicing--they simply plug in to the existing wire harness connection.
Replacing the Sensor
Warm the engine up for a couple of minutes before you attempt to replace the sensor. This will expand the metal and make removing the sensor much easier. While the engine is running, spray a large amount of lubricant along the threaded joint of the faulty sensor(s) and allow it to soak in.
Disconnect the wire harness outlet from the sensor. The wire from the sensor runs about seven to eight inches from the sensor, and it is retained by a plastic clip, to prevent it from contacting the hot exhaust system.
Use a 22-mm combination hand wrench or an oxygen sensor socket and ratchet to remove the sensor. If using a wrench, insert the disconnect sensor wire through the box-end side of the combination wrench. If using an O2 sensor socket, insert the wire into the slot on the side of the socket. Turn the sensor counter-clockwise until it is loose. The sensors only have four to five threads, so it won't take much to loosen them enough to be removed by hand.
Apply a very light coat of anti-seize compound to the threaded section of the new sensor. Most direct-fit quality replacement sensors may already have a light coat on the threads. Be sure, if you have to add some on, that you do not get any on the thimble-shaped sensor--only a very light coat on the threads.
Thread the sensor into the port by hand at first, so that you don't cross-thread it. Tighten the sensor snugly with the wrench or socket and ratchet, but be careful not to over-tighten it. Since it only has four to five threads, sensors are very easily stripped out by over-tightening.
Plug the wire harness connection back together and re-secure the wire to the plastic retaining clip.
Resetting the Check Engine Light
Bring the Tahoe back to the parts store that sold you the O2 sensor(s) and scanned the trouble code for you. They will usually offer to reset the "Service Engine Soon" light for you. However, once the sensor(s) have been replaced, the computer will detect the new component and begin running through an inspection and maintenance (IM) self-diagnostic mode. This may take a few driving cycles to perform, as the engine needs to heat up and cool down repeatedly. Once the IM monitors have completed the self-diagnostic and detected that the new replacement sensor is performing its intended task, the on-board computer will turn off the "Service Engine Soon" light.
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