CEL Code PO420

Hi all:

I have a 98 Civic LX (Manual trans.) with 185k miles.

The CEL in my car just came on last weekend RIGHT after I filled up at Citgo so I thought it was bad gas since I did put the gas cap on properly. The car still drives perfectly fine. I took it to my mechanic and he told me that he pulled code PO420 and that I need a new catalytic converter and one o2 sensor and the repair estimate is $840! He didn't explain how he tested the parts but the following was printed on my receipt:

Perform Scan test on onboard computer, check for proper battery voltage, battery connections and ground connections. Remove any stored codes and perform a PID check to confirm problems when possible. Retrieve code PO420 from Memory. Code Description is "CAT Efficiency below threshold. Bank one o2 sensor failure." This vehicle will need the catalytic converter replaced with one o2 sensor.

I just spent $600 on a timing belt and brakes so I am unable to fix it for a month or so. I asked if I could have the sensor replaced first and then the converter and he advised against this and said that one will cause problems with the other. Is this true? Everyone always says that females get scammed but I feel like my mechanic has been very trustworthy.


I also have to go to Boston next weekend (about 90 miles away). Could I safely drive there and back and would it be better to take the interstate or back roads? Sorry for all the questions! Any help would be MUCH appreciated.

Go to Ebay and look for an 02 sensor there, shouldn't cost more than $50 off of ebay. For the cat, just try to find the cheapest factory one that you can.

Installing either is easy. For the 02 sensor it's basically plug and play, if you know which sensor is bad. For the cat, it's just bolt on. Won't take more than a couple hours I guarantee it.

Go to Ebay and look for an 02 sensor there, shouldn't cost more than $50 off of ebay. For the cat, just try to find the cheapest factory one that you can.

Installing either is easy. For the 02 sensor it's basically plug and play, if you know which sensor is bad. For the cat, it's just bolt on. Won't take more than a couple hours I guarantee it.

Thank you for the reply, but I don't know enough about cars to install the parts myself. Wish I did!

I would find out if he would install the parts that you buy then. Cause he really is ripping you off.

Most mechanics charge about $60/hr for labor. Replacing an 02 sensor and cat shouldn't take more than a couple hours, they aren't hard things to replace. That means, he's charging you about $720 in parts and that is ridiculous.

yes u could drive the car and be ok. since u'r computer sees that problem, it will put itself into "safe" mode and run engine "gentler". u will notice a decrease in fuel economy though.

Thank you. I feel better about driving it to Boston now. :)

Update: After driving 120 miles, the CEL turned off by itself. Hope this is a good sign.

smae thing happened to me. i was ignorant at the time and payed $500 to fit it.

Update: After driving 120 miles, the CEL turned off by itself. Hope this is a good sign.

Just cause the CEL is off doesn't mean it's not still throwing the code. When my car had it's CEL, I went to an autoparts store to get it scanned. After that the CEL turned off, but it was still throwing the code, good thing to otherwise I don't think I would have been able to get it fixed under warranty.

it will still throw a code. the only way you can change that is by reseting the ECU.

you may want to get a new O2 sensor. otherwise yiou make just ruine your Cat. (the bad sensor with often make the cat malfunction and eventually break.)

fix the sensor befor you need to get a new Cat.

Thanks. I'll take it to Autozone to see if it's still giving the code. If it is, I will replace the o2 sensor.
(with 185k miles on the clock I don't have to worry about any kind of warranty!)

I just had the same code happen on my 98 ex, w/90k miles, and we ran the code ourselves and after we replaced the o2 sensory by the cat it fixed it... I don't think the catalytic converter should fail after 90k, I thought they were designed to last the life of the car? I'm not sure about 180k though, it probably does need to be replaced...

Don't ever think that things are not supposed to fail.

I made that mistake, figured buying a new car I wouldn't have problems with it for a few years. Replaced the cat at 15k, replaced it again and got a new short block at 32k, replaced water pump at 33k and getting a new cd player from them within the week.

your cat went out after 15k miles??? jeez... that's crazy

your cat went out after 15k miles??? jeez... that's crazy
yup, fucking Nissan quality. I'm never going to buy another Sentra.

... I don't think the catalytic converter should fail after 90k, I thought they were designed to last the life of the car?...

the ONLY things on a car that are designed and warrantied to last the life of the car are the seat belts. and that's not even always true anymore. if you have an active seatbelt restraint system, and get in a wreck those are done. (not talkin about airbags) but at the same time if the car is totaled, then they did last the life of the car so i guess it still stands.

ohk...the only thing that supposed to last "cradle to the grave" are airbag and anything concerning the airbags...most companies will warranty faulty aig bag equip....Second...you dont "reset" your ecu...you clear the code, erasing it....the only time you "reset" your ecu is when u clear the kam, or disconnect the battery...then u have to go through the relearn process which can take weeks for your o2 readiness, cat, and fuel curves, your cat isn't considered "cradle to the grave" most manufactures warranty a cat for x amount of miles, considering it should only fail if your engine is not running in tip top condition....but if your car never acts up...it should last a long time..., as for the shop u took it too....all that stuff he "did" was bs...he cleared a code, wait for it to come back, look at the secondary o2 pid, and said "if i throw a cat and 02, it'll be ohk" even if all u really need is an o2....so try the o2 first...and then see what happends....

96 honda civic lx. cat was gone after 85k miles.