Had couple codes indicating 02 sensors. went ahead and had all 4 changed out. Had to do it in two goes however. After they replaced 1 sensor, my codes disappeared except for one pending code. They finished putting the other 3 in today. On the way home, my ultra guage lit up and shows 0135, 0155, 011, 0161. Any ideas what has happened? This is after we just finished a head gasket, new wires, plugs, cam, whole nine yards. Also replaced MAF earlier. What could have happened?

 

Either you have a wiring problem or your O2 were bad out of the box.

 

you should also be using factory, genuine Bosch replacement parts. The Bosch system struggles with cheap, aftermarket sensors like those for oxyen, mass air flow, cam position, etc. The Bosch parts are about twice the cost of aftermarket, but there are too many testimonials of cheap parts causing abundant fault codes and just making problems much worse.

 

Assuming you used Bosch and put the front sensors up front and the rear sensors in the rear, it took a while for my ECU to cycle and clear the light and codes. In other words, the results are not instant. The computer needs time and mileage to reset with the new sensors. As far as new codes, yes, you want to check for defects or issues. The old codes are what I am referring to.

 

Well, I don't think they were Bosch so that is probably my problem. However, if the mechanic put 2 in the wrong places would that do it? Because the fronts are different from the back are they not? considering after he replaced 1 and I was down to only 1 pending code, I'm thinking I only had one more bad 02 sensor. These codes didn't come until the last 3 were put on.