How-To: Disable P0420 CEL code for life!

[shaeet]

DISCLAIMER: I am in no way promoting the pollution of our environment and destruction of our planet by posting this "fix". If you care so deeply about pollution and the impact of greenhouse gases on our planet, then by all means pay $1000 for a new catalytic converter if you have this CEL as it is the bonafide way to rectify the problem. I also disclaim any damage, fires, explosions and deaths this mod may cause to you or your family I replaced my rear oxygen sensor with a new Denso one off amazon.com last night & within 5 minutes of driving, the stupid CEL comes back on. The previous owner claims he had the dealership replace the cat, but when I was under the car last night, it looked pretty original to me.I did a few searches on here & MO.com and see its a very common problem for you guys too. I think its an issue with all 1ZZ powered cars. Replacing the cat will most likely fix the issue, but we are talking $200-1000 depending if you go aftermarket or OEM.I had this issue with my 2000 Celica back when I first bought it & completed this fix to get rid of the CEL for good. The fix is quite simple: Trick the ECU into thinking everything is normal with the cat.Engine Code Background:The P0420 code "Catalyst System (bank 1) Efficiency Below Threshold" basically means the front O2 and rear O2 sensors readings are similar, which is bad. Why? Because the catalytic converter is supposed to change the exhaust gases. The two oxygen sensors readings are supposed to be different. The rear oxygen sensor is a 4-wire heated unit. There are two black, a white & blue wire. They are:White: reference signal from ECUBlue: output signal going to ECU2 black wires: 12v heater element power & groundThe signal we are worried about is the output signal, which is the signal the O2 sends to the ECU. The fix is quite simple, install a 1000ohm resistor inline to this signal.PROCEDURE:First off you will need to part with a dollar to buy some resistors, unless you already have some from previous projects (like me!). Step1: Go to Radio Shack and buy a 5-pack 1000ohm 1/4 watt resistors (Part # 2062351): $0.99. Linky to Part. You will also need some electrical tape and/or soldering equipment and/or (removed) connectors to make the connections. You will also need something to cut the wire on the sensorStep2: Remove the negative battery connection from the battery, 10mm wrench or socket required for this.Step3: Open your passenger door and remove your floormat. On the left-side (under the dashboard) remove the black circular plug holding the carpet in place. Pull up on the carpet a bit & you will see a black-sheathed wire going to the floorpan. Thats your rear oxygen sensor! Unplug the gray plug, should be quite easyStep4: Pull back the black sheathing, you should see the 4 wires, one blue, one white, two black.Step5: Cut the blue wire! Step6: Install the resistor. There are numerous ways to do this depending on how lazy you are. SOLDER: If you want the most solid connection, strip a bit of wire from both ends of the blue cable, and solder the resistor in between them. Cover with heatshrink or electrical tape.CRIMP: The next-best connection would be to cut back some of the wire and crimp some (removed)-connectors to the resistor and then bridge it between the cut wireTAPE: The quickest and easiest, and also most likely to fail in teh future (and the way i did it b/c i'm lazy) is to simply take the resistor, and shove the ends of it into each side of the blue wire, and then heat shrink or electrical tape over it. Make sure the blue wires aren't overlapping the resistor, you want the signal to travel THROUGH the resistor, not around it. Step7: Plug the oxygen sensor back in, replace the carpet & black plug thing & floormat. Re-connect the negative battery terminalENJOY! Shouldn't have the CEL light ever come on again from now on & your car will run perfectly fine because it will think the catalytic converter is operating properly.I did snap pictures of what I did last night, but was too tired to upload them. I'm writing this at work so I'll update with some pictures when I get back home sometime, but either way, the descriptions above should be sufficient for anyone to complete this "fix".

[jjhendri]

Ok, got the dreaded P0420 code this morning. I stomp on it at the traffic light and next thing I see is the CEL. So is it safe to say that I need a new Cat or replace the 02 Sensor after the Cat? Got 123,500 miles on it. Replaced the O2 Sensor before the Cat in April 2010 when I got a P0135. I have noticed in the last 3 weeks that my mileage is off about 3 mpg. Normally get 25-27. I now get about 23. Plugs were changed in 2009 (think about 80K or 90K).I've read all the post and it looks like a toss up..Any advice? I'm posting this to 2 areas of the forum.

[bx3_27]

Tried this out tonight. Unfortunately my Cel didn't go away. Do I need to get somebody to clear the code for me, or maybe drive a certain distance before it will go away? Also I noticed that in your post you said to use a 1000 ohm resistor, but the link you had posted was for a 1mega ohm. I bought both just in case but neither one seemed to do the trick. Any suggestions would be greatly appreciated. Thanks in advance.

[joatmon]

if you don't have a tool to check/clear CEL codes, people say you can clear them by disconnecting the battery for 15 minutes or so. When disconnecting the battery, I always do the negative lead, that way if I clumsily short the terminal to the car body or some engine part, there are no sparkssometimes cats go bad and just don't convert exhaust gasses. Sometimes they plug up. This trick might get you by if yours is just not converting, but if the cat is clogged, it's just ignoring a power and MPG theif.

[Salsa Guy]

To reset the ECU you can disconnect the battery (both terminals) then short the leads to the car. DO NOT SHORT THE BATTERY the leads should not be on the battery when this is done. Or you can disonnect the battery for 15 minutes (maybe more) then that will reset it also. THIS IS ALL DONE AT YOUR RISK!

[star_deceiver]

Quote, originally posted by bx3_27 »Tried this out tonight. Unfortunately my Cel didn't go away. The 0420 may have gone away but was that the only code you had?

[bx3_27]

Shorting the battery leads to the chasis worked like a charm. The cel cleared and I thought I had this problem licked but the cel came on again at 32 miles. I'm using the 1k ohm resistor, but I might try the 1m ohm since this one didn't seem to work. Then again I may just bite the bullet and take my car to a mechanic. My county requires that you pass emissions to get the sticker for your tag and I got a ticket about a month ago for not being up to date. The trooper who pulled me said that I could get it dropped in court once I pass inspection, but I'm quickly running out of time. If I get a diagnostic and find out it's a bad cat, does anyone know where I can order one for pretty cheap?P0420 was the only code I had when I got it inspected a few weeks ago, so it's possible that I have an additional code/s now, but I have no reason to suspect that at the moment.

[torker]

I have been searching for this fix too. I have the same code. I have been reading that you also have to change the value of the heater wires too, not just the signal. My car idles too high when cold but runs fine and still gets 27 mpg. average. Anybody have more input here? Do I need a 1Mohm or just 1Kohm?

[torker]

Bump, I know this has been covered but I am not having any luck using search to find info. Has anyone tried this? I really can't afford 750 dollars for a converter/pipe. I always check my mpg. so if it goes down I will have to do something I suppose.

[bx3_27]

You said you had been reading about this type of fix, do you have any helpful links to posts or articles? So far this post is the only info I've found on this type of mod.Also fyi, my vibe idles way high when it's cold too.

[torker]

I did not bookmark anything because the info I have found so far is pretty limited. I did end up finding some info on a Triumph motorcycle site and a Subaru site but the info conflicts. I am still searching.

[Sublimewind]

Quote, originally posted by torker »I have been searching for this fix too. I have the same code. I have been reading that you also have to change the value of the heater wires too, not just the signal. My car idles too high when cold but runs fine and still gets 27 mpg. average. Anybody have more input here? Do I need a 1Mohm or just 1Kohm? I wouldn't touch the heater wires... high current app, add a resistor create a massive amount of heat..

[torker]

http://www.audiworld.com/tech/eng53.shtmlFound a little more info. It seems that using a diode is a much better way to go. Since a resistor will limit current and not really voltage. I don't plan to mess with the heater wires. I did read where they can consume 25 watts and I think that mod is for when the o2 sensor is removed . I hope this works till I can afford another cat.

[star_deceiver]

Ever read up on these? http://www.amsperformance.com/....htmlPretty much relocating the 2nd O2 sensor out of the exhaust flow. Although most of the ones I've seen are homemade...

[torker]

Yea I might try that. I have heard of people using spark plug anti foulers. Thanks for the link. I also have a universal Bosch o2 sensor so I can make sure I have the right bung up front. I will let you all know how this goes.

[cshaffer750]

I used the diode as explained in the post from the VW forum. Worked for me, no more light. I tried the resisitor first and I'm not sure if I had a good connection or not, but the light would come on after 30ish miles