I have an 03 MCS. 60,000 miles. SES light came on my neghibor w/ a computer plugged it up and said o2 sensors were bad. I replaced pre and post 02 sensors. Reset the computer and about 60 miles later I got the SES again stating it was the pre o2. I am going to try to switch the pre and post to see if I got a bad part. My question is, What are the chances its the wiring harness? (It seems to be in good shape). Also if I reset the computer from the gauge cluster will that clear my SES codes or do I have to plug it in to a computer?

Thanks,
Brennan

 

Pull that O2 sensor and carefully wipe it off with a microfiber towel. Once you put it back in, try a different gas station.

 

If the PRE cat O2 is throwing a code...check to see what the code is....it is often due to running lean due to un- metered air...a leak.....find it, and the code will go away!!
The post O2 is usually due to a failing cat..
Were they OEM O2 sensors? A few techs swear that the aftermarket ones (universal) throw codes...and a few of the better techs here have said similar things....
And you must have an OBD-II scanner to read/re-set the codes.....and many basic ones cannot re-set/clear some codes!!

 

Thanks guy!
I just went and bought an OBDII Scanner.
They were Bosch Exact Fit Sensors.
Im going to Flip them and clear the code.
Then if the back one faults Ill know its a bad sensor.

Thanks Again