P0420 and Voltages at Sensors...Please Explain
03-11-2008, 03:42 PM
#21
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Matt,
I’ve been thinking about your P0420 ever since I read the P0420 CEL Code...Any Definitive Fixes Identified? post. I’m not sure that there is a difference between the 49 state emissions and the CA emissions 01-02’s. My under the hood catalyst sticker says it meets Federal and CA. I am the second owner and the truck is from Ohio.
I have a 2007 Mitchell Collision Estimating & Reference Guide that shows all 01-02’s have two cats. It also shows that the Toyota part number is the same for the front converter on 99-00 with CA emissions and the 00-02’s. In addition, there is just one part for the front cat and one for the back cat on the 01-02’s instead of the “w/ Calif emissions” option that is found on the 96-00 part numbers.
I had to replace the cats on my 02 due to a P0420 and used aftermarket brands. The code hasn’t come back (knock on wood).
Why don’t you cut the old converters off (taking as little of the exhaust pipe as possible), sell them for scrap and use that money to pay a muffler shop to install quality aftermarket units? With the money you make on the scrap sale you should easily have enough to cover the muffler shop bill. …With money to spare if you need the URD box because of the CA emissions.
I’ll try to dig up the info from my research when I was going through this.
I’ve been thinking about your P0420 ever since I read the P0420 CEL Code...Any Definitive Fixes Identified? post. I’m not sure that there is a difference between the 49 state emissions and the CA emissions 01-02’s. My under the hood catalyst sticker says it meets Federal and CA. I am the second owner and the truck is from Ohio.
I have a 2007 Mitchell Collision Estimating & Reference Guide that shows all 01-02’s have two cats. It also shows that the Toyota part number is the same for the front converter on 99-00 with CA emissions and the 00-02’s. In addition, there is just one part for the front cat and one for the back cat on the 01-02’s instead of the “w/ Calif emissions” option that is found on the 96-00 part numbers.
I had to replace the cats on my 02 due to a P0420 and used aftermarket brands. The code hasn’t come back (knock on wood).
Why don’t you cut the old converters off (taking as little of the exhaust pipe as possible), sell them for scrap and use that money to pay a muffler shop to install quality aftermarket units? With the money you make on the scrap sale you should easily have enough to cover the muffler shop bill. …With money to spare if you need the URD box because of the CA emissions.
I’ll try to dig up the info from my research when I was going through this.
Last edited by element; 03-11-2008 at 03:43 PM.
03-11-2008, 03:50 PM
#22
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Element...thanks for the help and keep me posted on what you find. I'd love to go aftermarket if I could...as long as I don't have to install the URD "black box.."
CGeorge...I'm at 186k miles so it's very possible that my cats are bad. All of this started around 150k or so. I am not going to install the "black box" for the same reasons you fear it. We do not do emissions testing in Alabama, but they do in Georgia. If I sold or traded my truck and it ended up there and the "black box" was found, they would probably trace it back to me and I be in deep you know what. It's not worth it. I hope that someone can prove or show that they have gone thousands of miles on aftermarket cats that did not cost $1,500. I'm not going to spend that. Until someone can prove this to me, I'm just gonna keep clearing the code when it rears it's ugly little head.
BTW...I have never replaced my MAF sensor, my before cat sensor, or my after cat sensor. I was under the impression they would throw their own code when they went bad. Heck, the coil packs started throwing a random cylinder misfire until they finally got weak enough and pointed to the coil pack for cylinders #2 and #5. Are these sensors the same way?
Matt
CGeorge...I'm at 186k miles so it's very possible that my cats are bad. All of this started around 150k or so. I am not going to install the "black box" for the same reasons you fear it. We do not do emissions testing in Alabama, but they do in Georgia. If I sold or traded my truck and it ended up there and the "black box" was found, they would probably trace it back to me and I be in deep you know what. It's not worth it. I hope that someone can prove or show that they have gone thousands of miles on aftermarket cats that did not cost $1,500. I'm not going to spend that. Until someone can prove this to me, I'm just gonna keep clearing the code when it rears it's ugly little head.
BTW...I have never replaced my MAF sensor, my before cat sensor, or my after cat sensor. I was under the impression they would throw their own code when they went bad. Heck, the coil packs started throwing a random cylinder misfire until they finally got weak enough and pointed to the coil pack for cylinders #2 and #5. Are these sensors the same way?
Matt
03-11-2008, 04:01 PM
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Matt,
I known there are a lot of opinions on here and a lot of people really believe that you’re O2, AF, or even your MAF could possibly cause this code. From all my experience with Toyota and other OEMs, P0420 is a bad cat 99.99% of the time. There is a very very very slight case that you could have a bad sensor but from the info you've provided I am 100% sure you have a bad cat (or cats in your case). You post sensor is switching and that only means one thing - bad cat. I've never seen any other failure that causes a rear O2 sensor to switch like you described. To turn your light off you need to replace your cats. If you replace just one then you've got a 50/50 chance of getting the right one and I guess you could try that if you want. Maybe look at aftermarket since the OE parts are so expensive. If you’re really crunched for money then put the simulator on and never worry about the 420 again.
I known there are a lot of opinions on here and a lot of people really believe that you’re O2, AF, or even your MAF could possibly cause this code. From all my experience with Toyota and other OEMs, P0420 is a bad cat 99.99% of the time. There is a very very very slight case that you could have a bad sensor but from the info you've provided I am 100% sure you have a bad cat (or cats in your case). You post sensor is switching and that only means one thing - bad cat. I've never seen any other failure that causes a rear O2 sensor to switch like you described. To turn your light off you need to replace your cats. If you replace just one then you've got a 50/50 chance of getting the right one and I guess you could try that if you want. Maybe look at aftermarket since the OE parts are so expensive. If you’re really crunched for money then put the simulator on and never worry about the 420 again.
03-12-2008, 07:22 AM
#24
air fule sensor voltage 101
The sensor’s output is not a changing analog voltage, but rather a small (< 0.020 amps) bi-directional current. Internal circuitry within the ECU converts the analog current output into a voltage. It is this converted voltage that can be seen on the scan tool.
This is why you cannot read the voltage at the sensor, it is within the ECU where this voltage lies. Newer scan tools can stream the voltage and waveform.
here is a link which shows good detail on setting up and testing a/f
http://www.babcox.com/editorial/us/us10226.htm
The sensor’s output is not a changing analog voltage, but rather a small (< 0.020 amps) bi-directional current. Internal circuitry within the ECU converts the analog current output into a voltage. It is this converted voltage that can be seen on the scan tool.
This is why you cannot read the voltage at the sensor, it is within the ECU where this voltage lies. Newer scan tools can stream the voltage and waveform.
here is a link which shows good detail on setting up and testing a/f
http://www.babcox.com/editorial/us/us10226.htm
Last edited by edzo; 03-12-2008 at 07:26 AM.
03-20-2008, 10:38 AM
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This has been a very informative thread. I have the same error code on a T100 that has a fairly new high-flow cat and new cat-back exhaust. The front 02 sensor is 4 years old with 20K on it, and the rear 02 sensor is stock (167K). I pulled the code yesterday at Checker, and I'll go back today to see if their scanner will let me see voltages while the truck is running...
In general, the month leading up to the Check Engine light coming on, my mpg had dropped by about 2. I cleaned the throttle body and air filter, tires are inflated properly, no obvious holes near the cat or change in sound, and the plugs/wires are less than a year old. I am guessing that my mpg drop might be related to a sub optimal 02 sensor, that is now finally bad enough to throw the P0420 code. But, from what I understand, that code will only be thrown by the rear 02 sensor being bad, or the cat being bad. If the rear 02 sensor was bad, it would not affect my mpg, right? And if the cat's performance was below efficiency, then that would mean it was not cleaning the exhaust gas well, which again would not affect my mpg. So, I don't want to hijack the original post, but I have the same error code and am wondering if attempts at diagnosis are being thrown off by a coincidental drop in mpg? I'll try to diagnose the switching of the 02 sensors and let everyone know what I find. In the meantime, any advice is appreciated!
In general, the month leading up to the Check Engine light coming on, my mpg had dropped by about 2. I cleaned the throttle body and air filter, tires are inflated properly, no obvious holes near the cat or change in sound, and the plugs/wires are less than a year old. I am guessing that my mpg drop might be related to a sub optimal 02 sensor, that is now finally bad enough to throw the P0420 code. But, from what I understand, that code will only be thrown by the rear 02 sensor being bad, or the cat being bad. If the rear 02 sensor was bad, it would not affect my mpg, right? And if the cat's performance was below efficiency, then that would mean it was not cleaning the exhaust gas well, which again would not affect my mpg. So, I don't want to hijack the original post, but I have the same error code and am wondering if attempts at diagnosis are being thrown off by a coincidental drop in mpg? I'll try to diagnose the switching of the 02 sensors and let everyone know what I find. In the meantime, any advice is appreciated!
03-20-2008, 02:59 PM
#26
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