On the I6 engine, there's only 2. 1 upstream, 1 downstream.
There may be four. Bank 1, sensors 1, 2 and 3 and bank 2 sensor 1. This link will help you find the sensor that you need.
https://www.youtube.com/watch?v=vAxuP9UVQPs
SOURCE: Possible o2 sensor 2002 GMC Onvoy
O2 sensors indicate unburned oxygen in the exhaust sysytem. Bad O2 sensors causes fuel mixture to run rich. It causes fuel consumption and your emmissions test will not pass. Check for vacuum leaks check the manifold.check for a misfiring cylinder, a burned exhaust valve that is leaking compression. replace the O2 sensor or sensors. Some cars have 2 . One for the intake another for the out take. If it reads a code for the Map sensor along with the O2. It is better ifyou replace both sensors. But I think that the problem lies in the oxygen sensor or sensors. Pleae vote my answer if this helps.
SOURCE: Need firing order diagram for 2002 gmc envoy
one, five, three, six, two, four
The plastic intake should have this sequence molded into it somewhere, and even the corresponding cylinder numbers in front of their respective holes. Have fun, and thanks for posting on Fixya.com
SOURCE: 2002 gmc envoy shuts off when i turn on the ac whil ideling
If it does it when idling I would suspect an IAC motor (Idle Air Control). If it is opening too slowly the added air the motor needs will not be supplied fast enough and the engine will kill.
It could be other things also but this is where I would start.
SOURCE: 2004 GMC Envoy check engine light remains
Leave 02 sensor alone ,it is doing it's job . It is heated up because of lean fuel mixture due to incorrect engine temp.,replace thermostat before looking further.
SOURCE: 2002 GMC Envoy Coil Packs / Coil Module Assembly's going bad
swap it with another and check the code again to ensure that it is coil pack 3. This car doesn't have adiquate sensors to diagnose this properly and may indicate the wrong coil. Yes this is comon, its happened to me and I have the same make and model.
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Gary I believe your Envoy has a straight 6 cylinder in it. If I'm correct you have two O2 sensors. The upstream one will be located on the passengers side screwed into the exhaust manifold or where the pipe comes off it. The downstream one will be under your vehicle on or close to the converter. Hope this helped you.
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