Bound to happen. I finally got my first P0420 code!

You put 12v to the sensor & you'll end up with an ash pile, most if not all the sensors energize with millivolts/milliamps...

 

The O2 sensor will generate it's own low voltage, just like a knock sensor will generate it's own as well. Do NOT connect 12V to either side of the signal wire or you will damage the sensor.

Trust me, I know all about the code. I have dealt with this code on several manufacturers over the years. In my case it is a solid code, but my truck rarely is driven in the exact manner for the code to set live, which is the best time to test for the failure. Yeah, lots of possible things including bad fuel, poorly running engine, exhaust leaks, bad injectors....the list goes on and on.

 

At 65k, my 07 Highlander (4cyl) popped this code; I'd just driven thru torrential rain, and mostly avoided a huge puddle (small stream) that cascaded water underneath.
At 7 years, the post-cat 02 had enough and popped the light; went off promptly, was ok for a month, popped again.
One bath too many as had driven thru many and guess the shock to the sensor was fatal. Still under 8/75k warranty, and dealer paperwork showed a charge of $350 or so to switch it.
(That's about $200 less than non-warranty full price.)

 

Something that doesn't solve the code necessarily, but works to clear the code if you are broke and can't afford a new cat is to use spark plug arrestors, one drilled out to fit the O2 sensor, then installed like this. It moves the O2 sensor just far enough out of the exhaust stream to not pull a CEL.

(not my pic)

 

My apologies if this has been covered but I am throwing bank 1/2 and 2/2 both ?. I managed to clear the code and have it gone for a few weeks but it's back again and of coarse I am due for inspection now. CA has switched to OBD2 reading only with visual inspection so no more sniffer but two questions :

1. Could I simply erase the codes a few mins before going to the inspection and get by the ODB2 portion that easily ? The code never comes back for approx 20-30 miles...

2. It seem odd that it is reading both 1/2 and 2/2 at the same time ? What are the odds of both O2 senors or both cats being toast at the same time ? Bama - does the dual code lead you believe any specific symptom ?

 

When they check your system for inspection, if the place is worth a darn, they will check to see if the system has tested and passed. If you simply clear the codes then usually they will kick it and tell you that you can't pass until the system has tested and passed. You mention two different codes, but there are about 8 codes for O2 sensors. I would need to know the specific codes before I even tried to guess at a suggestion.

 

My truck threw those codes after driving through a TON of salt/silt on the roads during winter for snow and stuff. I have a URD TCAI installed. I just took the MAF sensor out, saw it was caked it salt dust and grime. sprayed it with a 7$ can of MAF sensor cleaner from OReillys and I havent tripped a code since..and that was almost 2 years ago. I would always try to start furthest from the engine (most likely least expensive fix) then work my way in. I didnt read this whole thread so if you already stating something about this sorry for the double tap.

 

It is just two 420 codes, 420 Bank 1/2 and 420 Bank 2/2 so that represents both drivers and pass side rear sensors correct ?

Edit - A little background, 120k, MAF cleaned recently, throttle body cleaned recently & plugs replaced. All OE headers, y pipe, cats and sensors, sensors cleaned recently as well w/ proper cleaners.

 

P0420 is for the efficiency of the catalytic converter. It can be a bad cat, or bad sensors.

 

Just thought I would share, I got a PO420 code a while back. Cleared it 3 times and it would just come back. I was in Autozone and came upon a new product called Cataclean. Expensive, but decided what the hell, I'll give it a shot. I ran the whole bottle on a very low tank of fuel, and it's been over 6 months code free. My scanguage even shows the computer clears it's self emissions test. The product has my seal of approval!

 

In need of some guidance, beginning of October my truck threw a code P0430. Take it to the shop, they clean the maf. Week later it comes back on. Take it back they clean the maf and intake. Week later it comes back. They go to the exhaust and replace gaskets. Same night it comes back. Drop it off they change all the sensors. Day later light comes back but I have both P420 and P430. Mechanic calls this toyota hotline and says its the cats. Is there anything else I can look at before I drop 2k down the tube

 

There is no need to spend so much money on cats since you are not in CA, there are a few aftermarket complete manifolds on the market starting around $275 each and Magnaflow has a cool equal length header cat combo for $500 ish each. You can also purchase single cats for under $200 and have your stock cats cut out and replaced.

 

Spent $200 on both new rear sensors and replaced them earlier this week and have been 420 free for a couple hundred miles but my gas mileage is still awful...maybe the ECU needs a while to catch up and fix the mix ?

 

Personally I do not recommend deleting the cats, regardless of where you live. Sometimes it can get expensive to repair a vehicle the right way, but if you plan to keep it, and you want to take proper care of it, fix it right.

 

I was not suggesting removing any cats at all, quite the contrary all of the parts I recommended include new cats either included as part of the actual header or separate cat only. Magnaflow and Performance both make complete OE replacement headers that include a good cat in the proper OE location. The Maganflow is a nice real header with cat included properly and the Performance brand looks exactly like the OE header with cat included. The OE header with cat is $1,000 each...these are only $275 and $550 ish each. Summit racing carries both brands if you want to check them out. I was only pointing out that since he is not in CA he actually has the option to purchase and use them legally whereas in CA you can not because they are not CARB certified, they are all 49 state parts. The Magnaflow 4 cyclinder complete manifold is CARB certified though :/

 

I misread your post. Sorry about that. I thought you were in the group recommending to delete the cats. Sorry.

 

This is out of my manual.
"HEATED OXYGEN SENSOR
HEATED OXYGEN SENSORS INSPECTION
INSPECT HEATER RESISTANCE OF HEATED •
OXYGEN SENSORS
(a) Disconnect the heated oxygen sensor connector.
(b) Using an ohmmeter, measure the resistance between
terminals +B and HT.

Resistance: At 20°C (68°F):

Bank1Sensor1:5- 7Q

Bank1Sensor2:11 - 16Q

If resistance is not as specified, replace the heated
oxygen sensor.
(c) Reconnect the heated oxygen sensor connector."


I just did this test today, and my downstream o2 sensor was reading 13.5 but when I tested the upstream sensor, it also read 13.5. This really confused me because according to the manual, it should be in the 5-7 range. Upon further inspection I noticed a small tack weld before my cat which could indicate a muffler shop drilling a small hole, performing a backpressure test or an o2 test and then tacking the hole. So I am thinking at some point the upstream sensor was replaced with the same exact sensor used on the downstream side. Any thoughts? i have not had time to inspect the cat it self due to rusted bolts. I'll get to that this weekend.

 

According to your post, if you look at what I have highlighted, you were testing the HEATER circuit, which has no direct affect on a P0420 code. You need to find the process which tests the resistance of the SIGNAL output, which should be about 450mV with the engine NUT running.

 

You are totally right, sorry! I am learning as I go here so be patient with me.

How do i test for the 450 mV signal? is it possible without an obdII scan tool?

 

Just for anyone who may still be following....I believe I have resolved everything. Keep in mind, I have an 09 TRD with 300K miles, and have been riding for many miles now with a code reader connected. This code reader has the capability to display pending codes before the go permanent (shows engine light on dash), has a readiness test to show all tests pass, fail, or incomplete for Emissions, and display live data. I had all sorts of codes flying Mass air sensor, catalysts too low in bank 1 po420, 2 po424 and final. also p440. I first replaced MAF sensor, did not work. I started using fuel system cleaner since the fuel filter is internal to th tank as a part of fuel pump assembly. This helped quite a bit especially with the catlyst bank 2. I changed my PCV Valve helped even more. I replaced the gas cap, and I believe this also helped for passing the EVAP test. I started to realize that all of these issues seemed to be a part of combustion air flow drop, yet I change my air filters every time I change my oil. BUT, BIG BUT, on at least the TRD types, the breather has a flow straightner (or final filter, I think a straightner because I am a controls guy for my career) after the disposable air filter itself. It was frustrating that this filter/straightner doesn't seem to be able to be removed, so I sprayed it with some carb cleaner. Amazing results, but still occasional Air flow code, and PO420 catalyst too low bank 1. I took the breather off, and almost emptied a can of Carb cleaner on both the exposed side and into the opening where it attaches to air valve. even shook the fluid around by shaking the breather body. NO MORE MAF code even as a pending code. Keep in mind that before a code hits your dash, it will be in pending code for a while both time, cycle, and miles. Plus it is the yests that make you pass the emissions test. In fact, I have a green light for passing all the tests including O2 sensors and EVAP test complete, yet the catalyst too low was still throwing a code. Also, the EVAP test takes a considerable amount of miles, time and on/off cycles to complete. I would only erase codes once the went from pending to stored, since every time you erase codes, all the tests reset, and the EVAP one takes a long time. Well the bottom line here is that with restricted combustion air flow, anything that uses vacuum (EVAP) will give you a problem if your Combustion air is restricted since it is this air that creates the vacuum. Also, if starving for air, any other O2 sensor or catalysts codes can be affected. The only code I get now (and sometimes resets itself to okay before going to a stored code) is PO420 Catalyst too low bank one. Well the only way any of these Catalyst codes are developed are from the O2 sensors. one on each ex manifold and after the Catalytic converter. I have the new O2 sensors, waiting for the weather to be okay for the replacement, since I can see that my bank one sensor's value when reading live occasionally goes negative. I hope this helps anyone else. it just goes to show you that sometimes its not just replacing parts, and you have to look at the entire system. For instance, you could also have a bad spark plug cause an O2 sensor code. Anyway still going strong with engine running like new, as well as fuel economy at 301,858 miles. Oh, and the guy that said the metal flapper on fuel tank neck is important to the EVAP system is wrong. just look at the little hole tap that is above the flapper which is where the EVAP is pulling the evaporation of gas fumes from, and the flapper would need some sort of seal to make it bubble tight. The flapper is a check valve/backflow preventor safety so if you leave your gas cap off, and start driving the gas wont fly out. But I agree, over filling your tank could do damage to your EVAP system, which I never do anyway, since you can now have liquid gas get sucked into the evap system rather than just fumes. I am concerned about this now since my flapper check valve is missing. Good Luck. I know I'll pass my inspection coming in March at 300K +!!!