Gilly,


Well I disconnected my battery to reset the check engine light. I started my vehicle up and the check engine light is now not illuminated when I’m driving.

I did a little reading and it seems that the parameters the computer requires for the check engine light to stay off for a P0156 fault code are very narrow. So it may come on again soon; I really don’t know.

According to the code the O2 sensor on the drives side of the vehicle behind the CAT is the one that supposedly is malfunctioning. If I’m not mistaken it measures the exhaust emissions after they go thru the CAT. So one of two things is happening. Either the O2 sensor that threw the code is not capable of reading the emissions that are passing thru it as being within the parameters, or theO2 sensor in front of the CAT is not working properly either and therefore the computer is allowing an improper mixture which causes the O2 sensor behind the CAT to detect that the emissions are not within spec.

Since the vehicle is running identical to the way it was running before the check engine light went on it would seem logical that the O2 sensor behind the CAT is having trouble measuring the gases to tell the computer that everything is as it should be. To conclude otherwise one would have to assume that the O2 sensor in front of the CAT is malfunctioning, but the computer is not reading the fault from the O2 sensor before the CAT, which is unlikely.

I don't think the O2 sensor malfunction of the sensor behind the CAT can affect the way a vehicle runs unless the O2 sensor before the CAT is malfunctioning too.

Bottom line: There seems to be there is nothing wrong with the way my vehicle is running.

I am correct or mistaken in my analysis.