Thread: P0420 & P0136 Problem and How I fixed it

My check engine light came on when the car had less than 80K on it. I brought it to the dealer and they replaced the #2 oxygen sensor, bank 1. The check engine light came on shortly afterward. So I brought it back to the dealer. They told me it must be the Catalytic converter. I did not have it replaced because I thought they were wrong. I did not smell anything or see any smoke.

Later on the car would not pass Massachusetts inspection because the check engine light was on. According to the scanner the error code P0420 kept coming up. At 1 point an error P0136 so I again replaced #2 O2 censor and kept reading P0420. I then installed a straight cell fix and the check engine light did not come back on and the car passed inspection. The straight cell fix can be also hfound at O2 Simulator, mini catalytic Converter cel fix they also have a mini cat at that site but I didn't put out for the extra bucks, and besides, the straight cell worked great.

Nice I have an '03 Impala with a persistent p0420 code and I'd like to use 02 extender. But on these W-body cars the downstram 02 sensor is mounted on top of the exhaust pipe. So how did you have clearance for the straight extender? You can use the cheaper spark plug non-fouler thats drilled out but this link has stainless steel extenders that don't need to be drilled out. So it may be worth the extra price. Does anyone know how to get around the clearance problem?

I would rather just use an extender where the original 02 sensor is installed that can be removed later on. The original poster installed a straight extender on his Grand Prix. I was wondering if anyone else has installed an extender on a W-body. It doesn't look like there is enough clearance to even get a wrench or socket on the 02 sensor to remove it without droping the cat conv let alone to install an extender. Has anyone esle removed the downstream 02 sensor and installed an extender without droping the cat conv assembly?