does an '01 s40 have 2 O2 sensors?

[malcolm2]

I thought the 2nd downstream sensor was after the CAT. Isn't it supposed to verify the CAT is operating properly? My 01 S40 has 2 sensors on the down pipe. They are about 8" from each other.

I have a couple CEL p420 and p133. I had planned to put a CEL boss on the downstream sensor. Word is that will pull the sensor out of the flow and help the CEL situation.

420 is Cat eff below threshold. I thought the boss would help this, but it is in front of the CAT

133 is O2 sensor ckt slow (bank 1 sensor 1) This could indicate a bad sensor, right. My plan is to pull it and bench test it.

photo is looking down the exhaust pipe from the engine bay, see both sensors?

any other ideas?

[alschnertz]

Your 2nd sensor is after the cat. Yours looks just like my '01.

You realize your car has 2 catalytic converters, right? The first is surrounded by the sensors as you show. The other is under the passenger area after the flex pipe and before the 1st muffler.

[malcolm2]

Thanks. I saw the 2nd CAT with no sensors around it, so I figured that was it. I have never seen a CAT this close to the engine or in the downpipe. It is very small. But once I saw the 2 sensors, I went to work. I did not end up bench testing the 2nd sensor. I just removed it, added some anti-seize on the threads and mounted it in the CEL boss, then re-installed.

I went ahead and cleared the codes and will see what codes return.

[malcolm2]

CEL boss installed and codes were cleared on Saturday. I have checked the OBD port this morning, Wednesday, and I have no pending codes. The car has only been driven 40 miles around town prior to last night. I put another 40 interstate miles on it going to the Preds playoff game.

Fingers are still crossed. I might try to go get an inspection this evening, but want to make sure the ECU has gone thru enough cycles to pass....