ridetoofast

cat sys efficiency below threshold bank 1 ?!?!?
just had a problem before w/02 sens (bank 1) replaced sensor

Elton

try cleaning the maf sensor pull the efi fuse for a few mins and see if that clears it up

midiwall

You love giving that answer don't cha' Elton?


Mr. Ride... There's a SEARCH function here that will spit out more info than you could ever want. SEARCH on "P0420" (and those are zeros, not ohs) which is the actual code. Searching on "420" won't help much.

ridetoofast

unfortunately, and i say this because i ended up NOT needing it, but i've already replaced the MAF with a previous problem.

yeah i know/knew about the search, this board is v'bulletin (sp?) just like another board i use...shame on me for not using it.

midiwall

Basically, the code is a complaint that the cat isn't doing it's job. It's a result of the rear O2 sensor not reporting enough of a change compared to the front sensor. So... you're probably looking at replacing the _rear_ O2 sensor, or the cat. I'd lay better odds on it being the cat.

Your profile doesn't say anything about your rig, so I can't give you an idea if it's old "enough" that this should be expected.

I you do end up replacing the cat, go with an aftermarket high-flow. You'll appreciate the performance kick, and they tend to be cheaper than a standard cat. $56 shipped:

http://search.ebay.com/Carsound-Magn...MEFSRCHQ3aSRCH

ridetoofast

thanks for the heads up about the cat.
ive got a 99 sr5 4wd w/~116K on it

just recently did the following
fwd O2 sens
MAF
and thoroughly cleaned the throttle body
guess ill have to look into the cat

midiwall

You're probably due.

One thing that you could try and it wouldn't take too long to do, is to swap the front and rear O2 sensors, clear the CEL (pull the EFI fuse under the hood), and see if the CEL comes back. I wouldn't leave it like this, but it may be something to try that wouldn't cost you any $$$.

bwhyit

95% of the time it's a back CAT. I have hardly ever seen a O2 sensor cause this problem. The thing is your rear O2 has to actually be operating to say that the CAT isn't working. More than likely a CAT. If you have a scantool that will monitor the front and rear O2 voltages I can tell you a way to figure out if you need a CAT very quickly.

ridetoofast

i have a code reader but its pretty basic. i do have a fluke though...
not to muddy the waters but mpg certainly is NOT an issue. i track my mileage religiously (every tank) and i average upper 19's low 20's with the occasional excursion into 22/23. my last tank was 21.15.

norcalsvx

i thought the 420 code was for smoking weed

ridetoofast

well it is but coincidentally enough, its also a cat code ...according to my Haynes manual

Sdkfz251/7

I have this code on my CEL as we speak. I replaced the front O2 sensor cuz it was reading very slowly. I thought I had it licked but the code came back. Now my mechanic is telling me its the CAT. Sure enough he wants to charge me for a test to see which CAT it is.

Ryan

Tofer

420 huh? your trucks just stoned....

Sdkfz251/7

Very likely my friend.
Ryan

dallison

same code on the wifes' 01. i need to seek this one out

tradergordo

Can you please post the way to quickly figure out if the CAT is bad with the scantool? I've got 420 right now, and scantool - both sensors are fluctuating between about .1 and .8 (slightly tighter range on the post cat sensor) while I'm driving, second one drops to zero pretty quick at idle.

I have no idea what to look for to tell me the cat definitely needs replacing. Seems the sensors are working though.

I ordered one of the cheap aftermarket CATs today because they are cheap and I figure I probably need it (and if I don't I'll probably need it eventually). Can anyone with experience tell me what I'm getting myself into? How hard is it to replace a cat on your own?

Thanks!
Gordo

warriors_03

Be careful that you don't have a CALI SPEC vehicle. The cats for those are expensive. If you look under the pass side and see 2 cats, its gonna get expensive. If your in CALI, then you have to go dealership because after market are not CARB approved. I had this light a month ago or so, and mine is starting to act up. Its just expensive as $%&^!

bwhyit

Engine running at operating temp. Tranny in P/N and hold the RPM at about 1500-2000 RPM for about 1 minutes. This will get the o2s nice and toasty to ensure they are operating. Continue to hold the RPM and look at the front o2 sensor voltage, you'll rappid switching front rich to lean (0.1 to 0.9 V) This is normal. Next take a look at the rear o2. This sensor should be pretty much flatlined somewhere between 0.1 and 0.9 (normally towards the lean side 0.1). You may see the rear sensor switch but it will be at a very very low frequency (~30 seconds). The key is to look for quick switching on the rear sensor. If it's flipping from lean to rich quickly you know the CAT is not stripping the HC out of the exhaust.

Let me know what you find out.

tradergordo

Thanks for the info. OK - maybe before when I was checking it I was doing something wrong, but I could have sworn the rear O2 sensor was jumping up and down (at about the same rate as the front O2 sensor) fluctuating between .2 and .8. But I was actually driving to work while monitoring the sensors so maybe that wasn't the best way to do it.

Anyway, I replaced my PCV valve, removed and cleaned my MAF sensor and replaced my air filter. Then I did the O2 monitoring the way you described. This time the rear O2 sensor while not exactly flatlined, was oscilating around .1 (but only going up and down by less than .1 (maybe .05) so close to flatlining. Is that normal? Its definitely not at all what I was seeing before. Does it make any sense that anything I did (like the PCV valve or MAF cleaning) could have resolved the problem? Or is it possibe that a CAT could be working OK some of the time but not all the time?

I can't wait to see if the 420 code comes back on. It seems like it takes a long time before coming back on after a reset. When I first got it, I reset, changed the oil, changed the spark plugs, and the 420 code didn't come back on for over a week. By the way, I've been getting about 10% worse than normal fuel economy, so I'll monitor that as well.

bwhyit

That o2 reading sounds pretty good. You may have to wait until the code resets to check everything again. You know you can't fix it if it's not broken. The only other thing I could think of is for you to check to o2 heater to make sure it's working. Actually I'm not sure what rig you have so I don't know if you have a heated o2. If so then let the vehicle sit for several hours and get cold. Plug your scantool in but do not turn the ignition on. Once you get to the datalist screen turn the ign on and watch the rear o2. Cold it should be around 0.4-0.5. After a few seconds you should see it drop to lean (~0.1)
Let me know what you find out. Good luck!