About 3 months ago my wife's 06 Accord 4 cyl 160k mi had the P0420 code. I replaced the rear O2 sensor with an Autozone Bosh one and it has been fine up until recently.

It would come back and then go off when she filled up her tank. She noticed it would come on at 1/4 tank. It did this "turn off when full, come on at 1/4 tank" jibberish about 3 times.

Now it came on at 1/2 tank...

I have never seen a CEL be fuel tank level dependent...I have read things from replacing the fuel cap, to replacing the cat has solved the problem.

Anyone run into this? Honda's are not my expertise...but I have worked on Mustangs etc throughout the years.

Things I can do to fix it?
-Get temp readings of the exhaust pipe and at the cat. Cat should be above 300*F to be considered working correctly? This true?
-Hook up scan tool and watch rear O2 sensor real time graphs??
-Replace fuel cap.

 

Converter Temp Checks - Check briansmobile1 video on catalytic converter diagnosis. He describes using a IR temp gauge to diagnose.

O2 sensor monitor - That's what I did on P0420 on a 99 Subaru Forester to confirm the O2 voltage swings were occuring. It should be a smooth signal w/ slow changes.

Fuel cap is cheap enough and you never know. Perhaps fuel vapor pressure could have enough effect to cause a problem.

good luck

 

Thanks for the response. It's funny you mentioned that video...that's what I stumbled across on youtube with the IR gun.

The 02 sensor reading seems OK. I'll have to double check what sensor I am looking at...upstream or downstream. Whatever one I was watching had a noticeable sine wave to it that did not seem all that erratic/ "out of shape"

I agree, fuel cap is cheap enough to try.

 

Well I looked into this a little today.

I have 2 codes...
61-1 ABS
Battery Voltage Malfunction

and

P0420

My wife drove an hour home from work, car sat for maybe 15min in 30* weather then I hooked up the reader. Car was showing Normal operating temp, but the IR gun pointed at the cat next to the O2 sensor was reading 160*F. I was not reading the heat shield either.

The 02 sensors I view on the data list of the reader is 02S12(V) and 02S11(mA)

Upon idle the graph of 02S12(V) would steadily oscillate up and down between .120 and .810. When I hold a rev to 2K they it would oscillate faster (makes sense), let off to idle and it flatlined for a good 15 seconds (that normal?).

There are 2 O2 sensors...what one is 02S12? Upstream or downstream?

 

So after a little more research, I think the 02S11 is Upstream (before cat) and 02S12 is Downstream (after cat).

Also that the post cat reading/graph should be relatively "flat" or stable if the cat is working correctly since the 02 reads the amount of oxygen in the exhaust compares to outside air? If the cat is working right then the amount of oxygen in the exhaust should be somewhat constant?

My 02S12 is fluctuating up and down like a sine wave.

 

S12 usually is read as (bank 1, sensor 2). Your Obd2 scanner is likely same.

An cyclic wave form on S12 indicates the O2 level is changing rapidly, as in no converter storage of O2. See youtube video by scottykilmer about cleaning catalytic converter. A little trouble to remove and clean, but a lot cheaper than replacement,... if it works.

I don't have a key for 2000 ABS codes, but I thought that 61-1 was a SRS code for driver's seat belt latch switch fault. Is your ABS light flashing this code?

good luck

 

Check fuel cap in my honda accord 2007 v6