4 total, two up steam of the cat and two down stream. not hard to replace, 7/8 open end wrench or a 02 sensor socket.|||4 Sensors Total.
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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%26#039;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%26#039;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 %26quot;Service Engine Soon%26quot; 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 %26quot;Service Engine Soon%26quot; light.
%26lt;/snip%26gt;|||I assume you%26#039;re doing this because you have a fault code indicating a problem with the oxygen sensor reading. Nine out of ten times the problem is not the sensor itself but a problem elsewhere in the engine, usually an air leak in the induction system. I%26#039;d suggest you check manifold pressure before throwing money away on an oxygen sensor you don%26#039;t need.
