Hi all just wondering which 02 sensor is the code p0140/01/01 is it the pre cat or post cat? I changed out the post cat sensor and Im still getting the code. Im going to change the pre cat next Thanks

 

01-01 usually means bank 1 sensor 1. But P0140 says Bank 1 sensor 2 which is the post cat. Check the wiring harness on the main harness side.

https://www.obd-codes.com/p0140

Bank 1 Sensor 1 would be P0134.

 

Well I changed out the pre cat sensor and drove around a bit and the code came back P0140/01/01. I checked the wiring to both sensors and their identical readings so its not the wiring. I did notice that the 1st O2 sensor pre cat, had a bit of black soot on it. Im wondering if I have a exhaust manifold leak? I took off heat shield and checked all bolts a few were a bit loose like 1 turn or less so I snugged them up. im going to check in morning, before work to see if I can see a leak. Thanks

 

Update I found a broken wire inside harness and repaired it and its fine now. I tested exhaust and I have a bit of a leak at the last back flange before going over to muffler. Interesting though I see both sensors seem to be working ok on my code reade. Although now I did get a P0170 code I cleared it and cleaned off some soot on 1st O2 sensor. I drove car for almost 200miles yesterday and now Im getting a P0420 code? Not sure if the small leaks in flange would cause the 420 code or not....Thanks

 

Update #2 After checking the exhaust for further leaks which by the way I found a small leak at back flange connecting to pipe to muffler which I sealed. I still was getting a P0420 code. so I deceided to try anti foulers for both O2 sensors. All seemed to be well but then I got a P171 code which is runing too lean. Cant remember if I mentioned in other posts I did get this before. So when I got to my destination I deceided to take out the 1st O2 spacer and see how it would affect it. While doing that for some reason I decieded to check the spark plug boots. I found the 3rd boot when pushed on clicked which meant it wasnt totally on plug. Bingo this was causing all my issues along with broken harness wire for post cat O2 sensor. Car runs good and now I get a Cat Ready on my code reader which I didnt before. It all makes sense now it was causing a miss fire bad connection on spark plug and therefore not burning all fuel in that cylinder properly and O2 sensor was picking it up and giving me all the codes. I removed post cat sensor spacer too. Going to change out plug wires when I get them tomorrow.

 

I changed out plugs and wires and now Im getting a P0420 code for the last bit. Ive tried running duralube cat cleaner and no luck. Ive put in some lacquer thinner and still getting the P420 code... getting stumped here somewhat....Thanks