P0140 Rear Cat O2 Sensor on high flow cat

[Steve Caroccia]

This is the 4th O2 behind the cat code. My problem is I was throwing this code ever since I put the 3"/3" Catco cat on about 7 yrs ago, only now it is getting progressively worse to where I cannot reset it by disconnecting the negative, and I need a TX inspection. 2001 Firebird 3.8. I also have the 3" S-pipe to a Borla exhaust, stock headers for now. I had the HPP3 tune and an O2 sim on the rear O2 sensor (the 4th O2 sensor is disconnected and replaced with a little module that is suppose to output a constant mV). I went back to the stock tune about a week ago and I just reconnected the O2 sensor this morning. I am trying to determine if the sim is bad, or using the HPP3 tune caused some coking on the 3rd O2 sensor to where the O2 differential is not moving and throwing the code. If the 3rd O2 sensor is bad, should I expect to get some other error code? Any other troubleshooting advice (I was suppose to borrow a Tuner that lets me track O2 readings, but that phone call has not been returned) or possible remedies besides installing a stock cat?
Thanks in advance

[Steve Caroccia]

Re: P0140 Rear Cat O2 Sensor on high flow cat

I am replying to myself. I am getting more confused with location. In the Haynes P0140 comes back - O2 sensor, no activity detected post converter left bank. Is this really post converter? I am running a sim and double checked the voltage with scan tool. Base is about 0.45 V and varied between 0.40 and 0.55. Another website says if the voltage stays between 0.425 and 0.475, then it will throw the code. So is this really the header O2 and if so which side is bank 2? And really stupid question, do I only have 3 O2 sensors on a 2001, each bank and 1 post cat?

[bigbrian442]

Re: P0140 Rear Cat O2 Sensor on high flow cat

Yes, A 2001 only has 3 O2 sensors. It will through a different code if one of the primary O2's is not responding. While your sim may be changing the voltage, it may not being doing it fast enough to satisfy the PCM. SIM's do go bad.

[Steve Caroccia]

Re: P0140 Rear Cat O2 Sensor on high flow cat

Check that, my O2 sim behind the cat is only producing 0.440 to 0.455 V. Way back when I did not nearly have this many issues, so I think my O2 sim is degrading, maybe the capacitor, maybe some of the resistors, etc. So who has a functioning O2 sim on a newer firebird and where did you get it?

[CorX98gt]

Re: P0140 Rear Cat O2 Sensor on high flow cat

just get your pcm tuned so the 02 sensor wont light up....I have a 3 inch dp on my grand prix gt and when i had the stock pcm in the light would come on for the rear 02 even tho i had a cat on it and there was no problem before i put the dp on.....put me zzp pcm with the egr and rear 02 deleted and no problems. Alot of car set a code with a different dp i guess its bigger so its not gonna get the same density in gases that the smaller one gave??