I have a 2007 Accord EX-L 4 cyl. I have had this car for 4 years now and about 3 years ago I got the P0141 message for the first time. I took it to my parents mechanic and he recommended fuel system cleaner and the problem went away. The check engine light would still come on but very seldomly, I think I went over a year before getting the error code again. I would treat it the same, with fuel system cleaner and replacing the air filters and I always fill up with Chevron or Texaco gas bc I heard it was the best.
Two weeks ago, I got the error code again and before I could treat it the battery died on me during the last big freeze that we just got. I ended up replacing the battery and I put a new ground cable in as well as it was draining the new battery. After that, the code went away but shortly came back as the P0420 code now. I have tried the fuel system cleaner but to no avail. Online forums suggest that it is the catalytic converter. Also, I took it to the inspection center and autozone for them to diagnose it and they both came back with only the P0420 code. They also said it was the catalytic converter, but when he checked the emissions he said that they were low. If the catalytic converter is going bad, would it not be bad emissions as well? Other forums have also suggested that the O2 sensors are bad and should be replaced. Should I replace both or just the downstream one? What would be the best course of action? I need help to pass the state inspection as it is due this month.
The error codes have always stated Bank 1. Idk if that helps. The car has 108K miles and it drives great. Idk if it is in my head but I have noticed a bit more lag in the car's acceleration on the highway, and I'm ironically getting better gas milage now. Thanks in advance.

 

Code P0141 is a fault in the electrical heater for the secondary (after catalytic converter) O2 sensor. If the code has not returned, the problem must have been a bad electrical connection that has resolved itself. It will likely return, but don't worry about this code presently.

P0420 is catalyst system efficiency below threshold. This fault is detected by secondary O2 sensor determining that converter is not performed per pre-established thresholds for storing/delivering O2 to clean up exhaust. Acceptable emissions w/ P0420 are not uncommon as the threshold is set low to prevent gross emissions before repair.

You can replace secondary O2 sensor, but this is unlikely to resolve the problem. Better to spend your money on inspecting exhausts for leaks and checking integrity of converter (shake vigorously and listen for rattling). If rattling is heard, converter is defective. Exhaust leak can cause P0420 to be presented. Fix exhaust leak.

You don't have any indication that upstream O2 sensor (actually an Air:Fuel Sensor) is defective (no code), so replacement is unlikely to affect emissions and P0420.

Bolt-on replacement catalytic converters are available from amazon, ebay, etc for reasonable prices. Reviews are favorable.

There are recipes for "cleaning the catalytic converter" on youtube, but most require substantial effort and not many garages would want to undertake this. Check Scotty Kilmer on youtube for some easy and difficult fixes.

 

Thanks,

I am trying to avoid spending all the money for a cat converter but if it needs it I will get one. I looked on YouTube and got a can of bg44k at a dealership and am going to try that out first. If that doesn't work, should I replace the downstream sensor first and then move on to the cat converter if that doesn't work?

Thanks for all your help.

 

No reason to replace AF sensor or secondary O2 sensor. There is no code indicating these parts are suspect.

You can buy a direct fit Magnflow converter for what those two sensors cost. OEM part is $450+ shipping and Magnaflow is $157. I doubt Magnaflow is as robust and durable as OEM. Your call.

good luck

 

How do I go about inspecting the exhaust system for leaks and what do I have to look for?

I put a fresh can of bg44k and the car drives better now but still has the light on. I'm going to try resetting it also and see how long it takes to come back.

 

Net cost to replace the cat with an aftermarket part isn't bad. RockAuto shows $135 for a Walker and SellYourCatsDirect will pay $95 for the old one. Probably $100 total including shipping, gaskets, and an hour's shop labor to swap it out. My wagon is on its third year of a Walker cat; no problems so far.

 

One way to look for leaks is to run a can of Seafoam through the engine. This produces prodigous amounts of smoke and an illusion of really doing somthing. Any leaks should be obvious.

good luck

 

The way I look for exhaust leaks is wad up a rag & hold it against the tailpipe when the engine is idling. Not hard enough to stall the engine, but enough back-pressure will make the leaks louder.

Have someone hold that rag while you crawl around & listen/look for leaks.

 

Ok so this is the update so far.
@TexasHonda I had already ordered a secondary o2 sensor so I went ahead and tried to replace it today. I ordered a Denso sensor which I heard was oem for Hondas for $50 on amazon. Also since it had given me trouble before I thought it best to replace.

Unfortunately, I had to go to work tonight and couldn't finish it through. I got stumped on finding the connector underneath the passenger seat. Any ideas on what the easiest way to connect it is on an 07 accord sedan?
There's several connections there and it looks like I might have to take the seat out to get to it.

I took the opportunity while I was under the car to take a real look at the catalytic converter. There's no rattling of any kind inside the cat. Some rattling in the housing that protects it though but it's just the cover. The cat is a little discolored but it's 7 years old and been through winters up north. The car was originally from Maryland if that helps. The couplings for the cat to the exhaust pipes show some signs of rust but still look very much intact. I will check for exhaust leaks tomorrow when I have a helper and after I install the new sensor.

Any other suggestions?

 

There are two covers over the secondary O2 sensor harness and a grommet attached to harness where harness penetrates the floor board. Disconnect harness from inside vehicle, push grommet down below floorboard, and feed harness w/ connector end through hole in floorboard.

You may need a special tool to remove O2 sensor. You may also be able to use a large open-end wrench and hammer to loosen/remove.

good luck