Q: check engine light is on have a 4.2 if it is o2 sensor what should it cost about on 2004 GMC Envoy

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light is on constant 122000 miles on car also rear window regulator not working would that cause back door and back window not to work also the roof does not work i replaced modular board in rear door that did not fix it someone told me rear window regulator is not sending message so that is causing all other problems could that be
(2) Answers
First question, the 02 sensors run about 65.00 at NAPA for each of them, should not be over 45.00 to install ONE not counting any diagnosis.
Second question, have the body module scanned for codes related to your other problems ie door, window and the sliding roof!
A problem with your rear window regulator will have nothing to do with problem with o2 sensor. These are 2 totally different problems.