jc007i

I have a 2007 4 cylinder accord with 89,000 miles on it. The check engine light came on this week and I checked the code which was P0420 (Catalyitc Converter). Am I going to need to replace the sensor, or the Cat itself? Also, I am supposed to be driving about 250 miles on Sunday, does this need to be fixed before I make that trip? Thanks.

hybridmiklo

This code is usually correct and the cat will need to be replaced. Its just showing the the cat is not working efficiently. As for replacing it before a trip, your most likely ok. I don't think the honda cats seperate like the cheap nissan cats do. (I work at nissan and sometimes the cat falls apart and gets sucked into the egr valve or back into the engine).

dude_123

Erase the code and drive it around, if it comes back on then the CAT has to be replaced. Sometimes the PCM picks up out of tolerance readings and illuminates the CEL. All I know if it requires to be replace it's going to cost an arm for it. There is no universal applications for your year model make.

00Red_SiR

In my experience its usually a faulty sensor that causes that reading so it may be cheaper to change that first before changing the convertor, and see what happens.

hybridmiklo

what the hell? your experience? Nah man. I work at a dealer and see this everyday. Don't waste your money on the sensor. Unless you have a bad *** scan tool, replace the cat. Clowns like the one above me are the ones who go to autozone and try to shotgun parts on their cars starting from what is cheaper.

Obviously the sensor works because it picked up the cats inefficiency. If you doubt it, take to the dealer and pay the 1hr diag and look at the printout of the cat waveform

00Red_SiR

What's funny is that you know nothing about me or my experience, if you did, you'd be thinking twice about what you said...clown.

When a sensor starts to go bad it often gives false readings about how the cat is functioning. Stock cats don't tend to go bad at that mileage but sensors often do and the cat usually goes bad AFTER a sensor has gone bad and the car starts running rich in limp mode.

Either way I'd check with the dealer to see if your car still falls under it's emissions warranty.

hybridmiklo

californias cat warranty is 8 year 80k whichever happens first. The ecm reads the output voltage of the o2 sensor to determine if the o2 sensor is faulty or the cat is.

If the o2 sensor throws more than 1v or less than 0 volts than the ecm will throw a code for the o2 sensor because those values are impossible for the secondary o2 sensor. Another common code on hondas would be the heater circuit since the ground side usually fails.

For the ecm to determine that the cat is the problem it looks at the switching frequency as wells as compares them to the primary. When that is out of parameters it will throw a code for the cat.

I dont care bout your 'experience' or who you are, but the advice you gave him was horrible. You don't tell someone to buy this part because its cheaper. You don't assume the cat is good because of the mileage. There are many variables that can cut a cat's life short. I do this for a living and have my smog license to go with it.

ShaunRR

Lets refrain from name-calling please, thank you.

00Red_SiR

I hear what you're saying and I know that's what the textbooks will tell you but my own experience of owning an automotive shop and using snap-on scanners has shown me that techs often rely too much on what a book or a scanner says. In this case, either one of us could be correct and you know it. That was all I was saying. Telling him to change out his cat without being sure that its the real problem isn't the correct to go about this. I agree that further diagnosis is required and I wasn't assuming anything, I was pointing out what commonly leads to cat failures and you know it.

apwhat

gonna dip my toe into this pool of stupid, pull the o2 sensor, and the cat.. look at them.. is the cat clogged, is the tip of the o2 sensor broken off? Anything out of the norm??

its free and might get you some answers.

DCFIVER

Na, youre likely wrong. There is a 1% chance that the O2 monitor ran and passed with a faulty O2 and then the Cat monitor ran and passed also with a faulty O2. Do you know how stringent theses monitors are now. This is not early obd2. This vehicle is tier2, ULEV 2. Owning a shop and using a tinker toy Snappy scanner means nothing. While I agree with you that simply throwing a cat on the vehicle with out making a determination of any other fault is not the right path, the probability that the O2 is at fault is slim to none. In this shop of yours, you must not work on a lot of modern Hondas. Typical lifespan for these Cats is only about 90-100k, so it is not unusual for this vehicle to need a cat at the mileage indicated.