Replacement of Downstream (Bank1 Sensor 2) O2 Sensor on 2003-2007 Accord
I took on this repair because my 2003 Honda Accord 2.4L (LEV) had developed a P0141 (O2 Sensor Heater Circuit Malfunction (Bank1, Sensor2)) code. Its also worthy to note that while I waited for my replacement aftermarket Denso 234-4797 Oxygen Sensor 
P0141 code on my OBD II device
for the low emissions vehicle (LEV) model, if you have the Ultra low emissions vehicle model (ULEV) you would need a different O2 sensor. The good news is that following my replacement of the O2 sensor, the P0420 cleared as well. I have now driven over 5000miles since this DIY repair with no codes.
Materials: 1. New O2 sensor, 22mm O2 sensor socket (not really necessary if your sensor is not rusted in, mine wasn’t. A thick 22mm spanner should be adequate), 10mm wrench and support stands.
My 22mm O2 sensor socket
1. Move the front passengers seat as forward as possible, then from the rear of the seat, peel back the floor carpet under it. This is to expose the connector of the O2 sensor. I was able to do this without removing the front seat.
Carpet partially peeled showing grey O2 connector
Carpet fully peeled showing the rubber grommet (black) attached to the floor in addition to the O2 sensor connector
2. Detach the O2 sensor connector and then remove the rubber grommet. Slide this through the opening in the floor which the grommet covers.
O2 sensor connector and grommet passed through the floor opening
3. Jack up the left side of the vehicle and suspend on support stands. Using 2 support stands; front and rear, will give you more room to work under the vehicle. Remember, never work under a vehicle supported by a car jack alone. Jacks can fail!
I guess you no what this is, no need for a title.
The O2 sensor attached to the catalytic converter with heat shield in place.
4. Time to get dirty, go under the vehicle, remove the plastic clips holding the O2 sensor wires to the underside of the vehicle. Remove the 4 10mm bolts holding the bottom half of the heat shield in place.
Heat shield off
5. Unscrew the O2 sensor using the O2 socket or 22 spanner, Some sources recommend running the engine for 1 min and then shutting it off to ease the loosening of the sensor. I didn’t do this and the sensor came loose with minimal effort.
O2 sensor out of catalytic converter
6. Harvest the plastic connectors from the old sensor wire and attach them to the new sensor wire. When doing this, place them at the same positions they occupied on the old sensor. Match the length from the connector to the rubber grommet on the old sensor to that on the new sensor, then use adhesive tape to ensure that the O2 sensor wire does not move back and forth on the new sensor.
Old and new O2 sensor side by side. Observe the plastic clips on the old sensor
7. Apply anti-seize past to the O2 sensor threads. This will ensure your new sensor doesn’t get locked up by rust. This Denso from this seller on Amazon
Anti-seize applied to threads of O2 sensor
8. Replace O2 sensor.
New O2 sensor installed on cat
9. Follow reverse steps. Clear your codes using an OBD device. If you have a P0141 and P0420, address the P0141 first it may take care of the P0420. Over 5000miles and counting since replacing this and no codes!
All done!
New rubber grommet fitted with plastic connectors attached!
How can I order one for a 2007 Honda accord downstream
So I had similar issues. I replaced a couple of air hoses and air breather tube to be sure as that fixed it temporarily but still continued to get the 0420 code so I installed the same Denso sensor on the cat like you, cleared the code but the code came back. Now starting to believe it’s really the cat that’s bad. No real drag on acceleration yet but maybe just a matter of time.
Yea, probably a matter of time. IF you have the bandwidth, you could bring the cat down for an inspection. A good cat should have no signs of degradation of the honeycomb structure and not have blockages… Maybe before going this route, have you troubleshot all the other causes of a P0420?
Haven’t lowered the cat as I figured that would be quite involved and problematic unless I had plans to replace it then and there. Replaced the spark plugs 33k miles ago with Honda NGK. Seems like the air filter is clean, nothing really dirty there. I replaced it 14,000 miles ago. Tried checking intake leaks with soapy water and saw no bubbles on the different hoses I sprayed. What would be your choice of action next? Mine is a 2005 EXL 4cyl with LEV. I’ve got 241k on it.
Update**I’ve been meaning to update this for a while, but since my last reply I must not have given the car enough time to reset the code. After a few days of replacing the O2 sensor at the CAT the engine light went out and I’ve not seen it return yet and I’ve been over 1,000 miles since replacement. I think it’s safe to say that it’s now fixed.
Beautiful news!
Have you changed your gas cap, threads may be worn, add vaseline or sealant tape to it, reset the check engine light and see if see if that fixes it?
Didn’t need to. Changing that O2 sensor fixed it.
Hi i have a honda accord 2007 4cyl with a P0133 code.
Iordered :
DENSO 234-4797 OXYGEN SENSOR
-Denso 234-9040 A/F SENSOR.
Are these the only two sensores i need to change?
thank you
Hey,
Thanks for reading. Just to check that you ruled out the other possible causes of the P0133 on this accord e.g. Inappropriate fuel pressure, faulty fuel injectors, intake air leaks, exhaust gas leaks…
The sensors you listed are for LEV models, those for ULEV are different. Check the small rear window driver side for the LEV vs ULEV stamp. Good luck.
Thanks for the post, after I changed the o2 sensor, I cleared the code but it came up again with an p0137 code what should I do nest? Thanks
Hi Ayuku, what was the initial code you had before the replacement and was it the only code?
Hi I replaced the O2 sensor and the cat convert and the engine light still stays on..
It still reads the po141 code
Hello,
The light should stay on until the car completes a number of drive cycles. After that, the light should go off.
Thank you, this worked great for my 2004 Honda Accord Ex. I had to trim the carpet a bit under seat.
Hi Steve,
Great you found it useful.
Cheers!
very good description. Excellent work. thank you. I fixed my O2 sensor on my 2004 Accord just as you described.
Dean Parmar
Thanks Dean. Great to know you found it useful. Thumbs up on your fix!
I dont have an o2 sensor as shown.. my catalyc is o2 sensor less. Where else could it be i cant find it
Thanks Alvaro for reading. What car and trim is this?