P0420 and P0446 code help

So i have an 02 3.4 that has both p0446 and p0420 codes i need advice where to start with diagnosing the issue and it also im having issues with idle. When i start it first thing in the morning it idles at about 800-1000 where it should and when it warms up it idles at about 12-1500rpm.

 

Try a new (OEM) gas cap if you haven't already, those two codes together sometimes point to a faulty gas cap. Could be other things too but thats a cheap and easy place to start

 

Ok i will try that but that wouldnt cause my idle issue im having would it?

 

I had just gotten these two errors together this past weekend. New gas cap did not help me.

 

The 0420 is likely a result of the 0446 which is pointing to your evap cannister vent/purge valves. A new gas cap may fix it, but in my experience, it's almost never that easy (But hey... people do win the lottery...). Start by using some tape to seal your gas cap tight to the filler neck. Clear the codes and if they stay cleared, you got lucky and a new gas cap should do it. If it doesn't then track down a wiring diagram and check your vent & purge valves. Likely one of them has failed.

 

Ok yes i will try that then. The new gas cap did not solve my issue as i expected that it wouldnt. I was thinking i have a vacuum leak somewhere because my idle is also the opposite of what it should be although i dont know that would cause those codes or not.

 

a bad or faulty oxygen sensor typically the bank 1 sensor can cause a p0420 code and also an idling problem

 

I've been meaning to do a write up on this since i successfully solved both of these codes fairly painlessly and mostly on my own. The short version, is that my 0420 code was a hole in my exhaust intermediate pipe right by the muffler. had a shop weld a new intermediate pipe in, along with a new 02 sensor. Problem solved. For the 0446, I slowly and methodically took out each purge valve (2 or 3 under the hood and 1 on the charcoal canister) and checked them for continuity with a multimeter and checked them, I dunno, to see if they were dead, with a pair of leads and a 9V battery. First off, with the battery test, if the valve is dead then you just buy a new one. If its NOT dead, then you gotta follow the FSM and blow into them and see if they are operating properly. This is a super simple test and identified that the valve on my charcoal canister was dead. I bought the new one at my Toyota dealer (these arent things you go aftermarket IMO) for like $70. Problem solved. That valve on the canister is pretty easy to get to but I wrecked the bracket it was on so i just zip tied the new one back on to a good piece of metal up there. All good now.


This was $74 on the McGeorge site, but my dealer matches the online prices when he can. FYI, from what I've learned, the charcoal canister SHOULD BE a lifetime part. They can go bad IF someone fucks up like by overfilling the gas tank multiple times. But with normal conditions, it should last, so i was looking to avoid replacing the whole canister. I also incorrectly read on here, maybe it was old threads, that you couldnt just buy this valve, only the entire canister assembly. That is false. Stay tuned for the write up, but would be happy to answer questions in the meantime.

 

My 02 V6 Prerunner with 180k just tossed a P0420 three weeks ago. I used my shop vac on exhaust and taped it to the rear exhaust pipe. Blowing air into the pipes I then sprayed soapy water along the joints at the rear 02 where I found a hole at the attaching flange and also the joints with the flange. I wound up with a new intermediate pipe, muffler and tail. So far this seems to have solved the code.

 

Is that valve on the charcoal cannister under the bed of the truck? I have the 446 code. Tested the one under the hood which seems to be working.

what's weird is the code takes four to six months to come up again once I reset it.

 

Sounds like the Purge Selnoid or Fuel tank pressure sensor may be working intermittently.

 

I applied 12v to the purge valve under the hood and it clicked every time... But your saying it might not work everytime in normal use? There seems to be no other issues besides the check engine... Idle is smooth, acceleration feels normal, starts normal.

 

the valve solenoid can click but if the seal does not seal and it leaks vacuum a code will be thrown. we are talking a very small amount of vacuum that the tank pressure sensor senses.

 

The click indicates the Selnoid is working. Circuit continuity and flow must also be tested.

 

Thank you. I'll have to do some more Testing.

 

yes, thats the valve, under the bed.

like others above said, connecting 12 or 9v to the valve to test is just step 1. if its not dead, you then need to blow through it to check and see if its operating effectively. mine clicked, but the seal was blown.

 

Update. So i have ran a cycle of cata clean highly recommended and it has now cleared the 0446 evap code so now i only have 0420. Could it be as simple as an 02 sensor. I would really rather not waste money on a stupid cat. But i need my CEL off to get inspection. Also i have a 0505 which is IACV. Where should i start with solving that issue.

 

Cataclean help clean the catalytic converter which is the P0420 Catalytic converter efficiency below predetermined performance.
P0446 is EVAP code Inability to regulate flow of fuel vapor from tank.
Are you saying Cataclean cleared an EVAP code P0446?

 

B1S1 is Air/fuel sensor
B1S2 O2 sensor monitors Cat= P0420

 

Yes which made no sense to me. So i replaced a coil pack i was assuming was throwing the misfire code and those are now clear as well. So now the only codes i have left are p0420 still even after the cataclean and the p0505