Jeep_junkie

Already searched the forums. Am I the only one who's getting a lazy oxygen sensor P1133 code on stock manifolds? The car is an 01 M6 TA. The problem is very intermittent - from what I can gather from O2 sensor data (screenshots attached), O2 B1S1 is switching just slow enough to prevent the oxygen sensor readiness monitor from setting, but not enough to turn on the MIL. Compared to O2 B2S1, the counts are much lower. I noticed the code would show up pending every now and then after I had the driver's side cat replaced. The upstream O2 sensors are brand new Denso units installed about 500 miles ago. Tried swapping the sensors from left to right but it didn't change anything. Both sensors were clean and free of any visible contamination from soot, oil, coolant, etc. I have ruled out any electrical issues. The only thing I can think of is that there might be a pinhole exhaust leak around the cat, but wouldn't it also be audible? Any help fixing this would be greatly appreciated as I need the car to pass smog this month in CA!

Jeep_junkie

Fixed it. Had to replace the borderline bad catalytic converter. It used to set a cat inefficiency code P0420 but I was getting around it by using a bad downstream O2 sensor. Replaced the cat and put the good sensor back in and problem solved. Moral of the story - can't skimp on repairs; just fix it the right way.

trex600450

How much were you charged for replacing the cats ?

I have an 02 M6 LS1 TA, with similar issue.

Jeep_junkie

I paid the local exhaust shop $200. It's a Catco CARB legal unit. EO D280-83 part number 612005. You might save some money ordering it from Amazon.

trex600450

This is for both CATS and the labor cost ?

Jeep_junkie

No, one side only. Do not replace the cats if you don't have a P0420 or P0421 catalyst inefficiency code. I didn't replace the passenger side cat because it hasn't yet triggered the above mentioned code, even though on a scanner the downstream O2 readings look like the cat is toast.