My car is code jumping! It's like playing wack-a-mole with error codes.

Anyway, last week I had P0420, catalyst sysmtem codes and replaced the Cat. That seemed to fix the issue..at least that code didn't return within a few miles of operation like it used to.

After driving about 150 miles on the new cat, the MIL relit and running the code scanner showed P0139 - O2 sensor slow response (Bank 1 sensor 2).

Which one is sensor 2? the one in the cat, or the one just below the manifold? If it's the one in the cat, where does it plug in? when I follow the wire it goes up into the floorboard by in the back seat area.

Any help or thoughts on diagnosis will be appreciated.

 

If this is the 4 cylinder, then it is secondary O2 sensor on the cat, see attached pic.

 

Very helpful, thanks.
I pulled the sensor. It looks like it was replaced recently, it's a Bosch. Is there a way to diagnose and see if it is good. It was replaced before I installed the new cat. Over heated maybe? Other than some discoloration, it looks fine...no buildup anywhere.

 

Oh. and it is the 4 cyl 2.4L engine.
Thanks

 

Took the sensor to O'Reilly and, on a hunch, the counter guy asked if I had the phone number of the Previous Owner. I did. He checked his data and discovered that the PO replaced the rear O2 sensor back in July and gave me a new one on warranty. Sweet!

If any of you saw my other posts regarding the P0420 error code, you saw that I replaced a bad Catalytic Converter on Saturday. I'm wondering if the old converter kept overheating and damaging the O2 sensors. Maybe this will help. At least I didn't have to pay for this one.

 

Having a similar problem with a 2005 Honda Accord EX, 2.4L. Was getting a check engine light suggesting that I needed to replace the O2 sensor on the CAT. I changed it out a week ago, but am now getting the P0139 error code. With a brand new O2 sensor there (OEM), what else could be the problem?

In addition, I was able to clear the code last week using Torque Pro, but today (a week later) this P0139 code won't clear. Any ideas why that might be? Is it coming back instantly? It won't even clear long enough to disappear on the dash.

 

Make sure the scan tool cable connections are tight and secure (i.e., the cable connector to the scan tool and the cable connector to the OBD-II port). Then try to erase the trouble code with the scan tool again. I had something similar happen a few months back due to the cable connection on the scan tool side.

If that is not the problem, and if the code keeps coming back, check for poor connection or loose terminals at the secondary heated oxygen sensor (HO2S) and the ECM/PCM. The wire harness connector for the HO2S is on the right side of the floor. The wiring from the HO2S leads to the ECM/PCM's at Connector E (a 31-P white connector). The ECM/PCM is located under the middle of the dash.

P0139 is secondary HO2S (Sensor 2) Slow Response.

 

I'm going through the same thing on my wife's 2.4. LX, right now. At about 112,000 miles it set Code P0141, heater circuit Bank 1, Sensor 2, so I replaced the original downstream 02 sensor with a Bosch. I haven't ever had any unusual problems with Bosch parts over the years, but...

Two weeks later the light came on again... Pulled the codes... P0139... so I replaced the Bosch with a Standard Motor Products brand. About three days after that, code P0139 is back again. I've looked around under the hood to see if I see or hear anything out of the ordinary. Nothing right off, and it still runs perfectly.

Today, I finally broke down and bought an OEM Denso sensor and will report back here with the results as soon as I get it swapped and the car through its readiness tests.

-Roger

 

Let me know how that comes out. I replaced mine with what was supposed to be the OEM Denso and still getting the "slow response" P0139 code. Wondering if it could be something else causing it. I've read where a vacuum or exhaust leak can also be causing the problem, but I don't appear to have an exhaust leak and I don't hear anything unusual under the hood. Also, can anyone tell me what temp the cat should be running at the front and rear of the cat? I bought a IR temp sensor to measure that and see about 100 difference between the two, but would like to know what it should be.

 

I installed the new Denso sensor last night, so my wife will start her travels this morning, and thus the testing begins. I will track the progress closely.

My original code being a P0141, "sensor heater circuit malfunction", was corrected by replacing the rear O2 sensor. That's when the 139 started, only with the new sensors, so it will be interesting to see how this plays out. I'll keep this thread updated of any changes.

-R