p0420

[mikeya]

I'm new to the site, not as experienced as most of you, but I'm learning. Here's the question: 1999 T4R, purchased used in PA, but it's a Cali vehicle, has 140K miles. It's been giving me the p0420 code - I've replaced both the upstream and downstream O2 sensors with Bosch (before I read you guys all say to use Denso - I'll get Denso next time). Anyway, the code still comes up. When I hook up the scan tool, I get a flat reading 640-650 mV on the upstream sensor and a fluctuating reading 250-550 mV on the downstream sensor - I think this is opposite of what it should be - makes me think I have two problems (1) a bad (new) Bosch upstream sensor since it's not fluctuating high and low and (2) bad catalytic converter(s) because the downstream sensor is fluctuating between high and low readings. Any thoughts would be greatly appreciated!

 

[SJC4Runner]

It is important to realize you do not want a "o2" sensor, you need a air/fuel sensor. This is what I got for mine. Denso 234-9002 Oxygen Sensor (Air and Fuel Ratio Sensor). The cheapest place I found for it was amazon at Amazon.com: Denso 234-9002 Oxygen Sensor (Air and Fuel Ratio Sensor): Automotive. Whatever sensor it is it will be expensive. It will not be a cheap sub 50 dollar part. My truck is a V6 Auto 4x4 limited. The sensor will be different I think if it's a different transmission.


This thread has a way to figure out what part you need.
Oxygen / AFR Sensors - Underdog Racing Development

The pertinent information:

2001 & 2002 4WD & 2WD V6; Front: 234-9002, Rear: 234-4261

2000 Cali 4WD manual V6; Front: 234-9001, Rear: 234-4153 2000 Cali 2WD manual V6; Front: 234-9001, Rear: 234-4155

1999 & 2000 Cali auto, 2WD/4WD V6; Front: 234-9002
1999 & 2000 Cali auto, 2WD V6; Rear: 234-4155 1999 & 2000 Cali auto, 4WD V6; Rear: 234-4153


1999 California manual V6 2WD/4WD 4Runner; Front = 234-9003
1999 California manual V6 4Runner; 2WD Rear = 234-4155 1999 California manual V6 4Runner; 4WD Rear = 234-4153

1999 & 2000 49 State 2WD & 4WD auto V6; Front = 234-4162 1999 & 2000 49 State 2WD & 4WD auto V6; Rear = 234-4162

1999 & 2000 49 State manual V6 2WD; Front: 234-4162 1999 & 2000 49 State manual V6 4WD; Front: 234-4161 1999 & 2000 49 State manual V6 2WD & 4WD; Rear: 234-4154




This might also help
http://www.toyota-4runner.org/3rd-gen-t4rs/81424-denso-o2-sensor.html#post699825

 

[Nelsonmd]

Here's my advice, ignore it.

Search this code on here and you will pull up tons of threads talking about this. Really it is a pretty straightforward code. Try replacing the O2 sensors, clean your MAF and TB, seafoam the engine, and if that all doesn't work, then you might need to fork over the cash for new cats.

I have had that code since I got the truck a year ago. I clear it when it comes up and ignore it. Plan to ignore it for as long as I can. Try to squeak by inspection by tipping the guy doing the inspection. Works for me.

 

[TheDurk]

Try to squeak by inspection by tipping the guy doing the inspection. Works for me.

That wouldn't work in NJ, I believe. The state's computer interfaces with the mechanic's computer while it is plugged into the vehicle's OBDII box. If the Trenton computer doesn't see good returns from the vehicle, no good sticker gets printed, only a FAIL.

Massachusetts corruption has obviously outpaced us. Pennsylvania has always had some talent in this area.

 

[mikeya]

I appreciate the help - thanks - hoping I won't need to replace the cats

 

[GottaBeTRD]

i think this was the code i got a few months ago and i put some Lucas fuel treatment in the gas tank, cleaned the MA F sensor and reset the computer and everything has been good since!

 

[mikeya]

Follow up

Here's some follow up on my initial post -

As I mentioned, I got a new upstream, and later a new downstream O2 sensor, both were Bosch, from my local auto parts store. This was before I got on this site and found post after post saying stay away from Bosch, use only Denso. Anyway, in addition to the new Bosch sensors, I cleaned the MAF, cleaned the throttle body, seafoamed it, did everything I could short of new cats. My CEL came on after 50 miles each time. My dealer quoted $2500 for new Toyota cats, and the local mechanic quoted $850 for aftermarket cats.

I gambled another $135 and got new Denso upstream and downstream O2 sensors from Amazon.

Bingo! I've gone over 1000 miles with no CEL, and no codes on the code reader!!

I am very thankful for all the input from you guys, you saved me hundreds or more!!

 

[SJC4Runner]

Glad to hear your problem is solved

 

[TheDurk]

Here's some follow up on my initial post -



I am very thankful for all the input from you guys, you saved me hundreds or more!!

Good to hear. Where's that guy who claimed to be a Toyota tech that said O2 sensors can't cure a P0420? It worked for me, it worked for you, and could have worked for who knows how many people that got ripped off for new cats at stealerships. And how many more ripped out perfectly serviceable cats and put in aftermarket ones that can't do the job. Really fries me.

Thanks for posting back.

I have gotten two P0420 in two-and-a-half years since I changed my rear O2. Both came when I drove at very slow speed for an extended period of time and the cats could not heat up. One was beach traffic, and the other was a crowded park with a 15mph speed limit. Cleared them, and they didn't come back. So don't be surprised if it happens to you.

 

[Stick Figure]

Good to hear. Where's that guy who claimed to be a Toyota tech that said O2 sensors can't cure a P0420? It worked for me, it worked for you, and could have worked for who knows how many people that got ripped off for new cats at stealerships. And how many more ripped out perfectly serviceable cats and put in aftermarket ones that can't do the job. Really fries me.

Thanks for posting back.

I have gotten two P0420 in two-and-a-half years since I changed my rear O2. Both came when I drove at very slow speed for an extended period of time and the cats could not heat up. One was beach traffic, and the other was a crowded park with a 15mph speed limit. Cleared them, and they didn't come back. So don't be surprised if it happens to you.

Mine always comes on at lower speed situations like that. Usually out on the rocks. Problem for me is it took a couple tries to pass the actual smog test last time even with a warm truck, so i know its the cats that are having some issues. For now i picked up a cheap scan tool to keep in the truck to make sure the CEL is for that code and not something more serious when i'm out in the middle of nowhere.

 

[TheDurk]

Mine always comes on at lower speed situations like that. Usually out on the rocks. Problem for me is it took a couple tries to pass the actual smog test last time even with a warm truck, so i know its the cats that are having some issues. For now i picked up a cheap scan tool to keep in the truck to make sure the CEL is for that code and not something more serious when i'm out in the middle of nowhere.

Fortunately, here in NJ, as long as the CEL is off and the tests are complete, you are good on emissions. (I have a Cali. rig). No additional sniffer test for OBDII vehicles. I think Cali. is the only place that does that.