codes p0420 and p0446 99 4runner

Discussion in '95+ Gen Toyota Trucks' started by bcstoy, Nov 24, 2012.

  1. bcstoy


    Feb 26, 2011
    I thought I share this experience with the forum. I was given the chore of bringing a 99 4runner back to life. The engine lost compression and was hard to turn with a wrench. Trying to make it run someone messed it badly. Fuel tank and pump wiring was all messed up, so were the EFI main relay and the cicuit main relay. I installed the motor out of a 2002 2wd tacoma and could not figure why it refused to start. In the process it gave codes for the MAF and ignition circuit. I figured those out and still it did not want to start. I had to check the wiring related to the pump and then I realized that the pump wires were crossed with the fuel sending unit wires. I also decide at that point to dump the newly installed airtex pump and replaced with a Denso pump (higher quality and smooth). Even the filter was installed backwards!. Finally the truck came to life and it began running on its own. I still had starting issues but those were my own fault for not tightening the auto tranny shifter and having the plug for the NSS loose. I got those out of the way and the MIL came on and from there it stayed on. My cheap scanner indicated p0420 and p0446. I read some good stuff in the forum, but as usual things do not exactly apply. I checked all the VSVs (2) and they clicked when given battery power. They also had continuity. Inspection of the lines going to the canister were also in good shape. At that point I thought about buying another used canister assembly. Then I started inspecting all the wires related to the evaporator system and bingo the PNTK wire for some unknown reason seemed opened. This is the middle wire that goes to the evap pressure sensor. At that point I knew also that the PS was good since I tested it in my Avalon (same system is used in early avalons). Thus I decided to run a parallel wire to the PS the moment I did that the engine light turn it off on its own. Both codes were gone!. I installed that bridge permanently. Now the PCM gets the right signal from the PS and can activate both VSVs accordingly. I may add that this 4runner is on its second engine and I suspect that someone may have caused internal damage to the wiring. The owner (relative) complained to me that the MIL was always on and they fooled it from time to time just to meet CA emissions. I learned a lot on this project and now the 4runner runs smooth as it should. I may add that current toyota's wire harnesses are not match for the old ones used in the first and second generations. All the stuff is brittle especially since the harness is running over the 3.4 block. And that could have caused the wire to go rogue. I thought that my experience may help someone, particularly when the canister is over $400 at the dealer. I wish I had taken pictures but there is no time for that when chasing several gremlins simultaneously. I found it interesting that this problem could have easily driven me into an expensive fix, i.e. catalitic, 02 sensors, and canister replacement.
    Last edited: Nov 24, 2012

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