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2002 2.4L P0420 code help please

Discussion in '1st Gen. Tacomas (1995-2004)' started by BigLad0331, Jan 24, 2023.

  1. Jan 24, 2023 at 8:17 PM
    #1
    BigLad0331

    BigLad0331 [OP] New Member

    Joined:
    Jan 24, 2023
    Member:
    #416288
    Messages:
    2
    First Name:
    Jordan
    Vehicle:
    2002 silver tacoma pre runner 2.4L
    Spacers and exhaust
    Hey guys. Brand new to this site and I’ve been stumped with my truck for over a month now. I have a 2002 2.4L and I’ve had a check engine light ever since I put on a mbrp cat back exhaust. It keeps popping a P0420 code and I’ve fixed everything associated with it including 2 new cats and 2 new o2 sensors. When I first put on my exhaust I ran out of time since I’m here on camp pendleton and the skills center I was using was closing. So I ended up straight piping it pretty much with a pipe behind the first cat that had a port for the downstream o2 sensor. Made it back to the barracks without a light and then drove it again and the light popped which I figured it would. Ended up getting on the exhaust and everything right the day after and the light still stayed on. I thought driving it would fix it. I was thinking I might’ve fried the sensor but didn’t realize that till now. Took it toyota got a new cat the 1st stage to be exact. It stayed off for about a week and then came back on. Took it to a muffler shop to get a new downstream o2 sensor and 2nd stage cat welded because it seemed like the only option. Got that sorted and it stayed off for a day before coming back on. Muffler guy was super cool and ended up getting my truck scanned by a mechanic next door and it said slightly low voltage in the downstream sensor. Replaced it for free with another on from o Reillys and it came back on about immediately. Ended up replacing the upstream sensor and it came on again after the light was reset. Been stumped on this. Few things to keep in mind. Downstream sensor was an oem one from Toyota before being replaced by the muffler guy with a denso one. Upstream was a denso and was replaced by a denso. Front cat is oem from Toyota, 2nd cat was welded on with a cali carb legal from magnaflow. When the mechanic scanned my truck both cats were reading very good. So no problems there. Mechanic recommended flashing the ecu. What I’m thinking is my downstream o2 sensor needs to be oem from Toyota since it was originally like that. I feel my ecu is reading it with the voltage being off and popping the code. I also asked a few other mechanics over here and they said to take it to Toyota since tacomas are pretty specific about toyota parts especially sensors. Just wanted an input to what anyone thinks before I try anything. Also to note truck runs pretty much perfect besides a slight low idle sometimes but it’s always almost had that. I also think it might be the downstream sensor since I know that one has nothing to do with air/fuel mixture and can trigger the cel with a P0420 code. Thanks in advance to whoever replies!

    0037C6D0-2B40-454E-9CA7-FE634698C9BE.jpg
     
  2. Jan 24, 2023 at 8:22 PM
    #2
    02hilux

    02hilux Don't follow me, I'm lost myself

    Joined:
    Sep 14, 2016
    Member:
    #197244
    Messages:
    3,773
    Planet: EARTH
    Vehicle:
    Point & Go
    Too much to read. Make sure there's no exhaust leak
     
    1bad2k and JasonLee like this.
  3. Jan 25, 2023 at 7:00 AM
    #3
    BigLad0331

    BigLad0331 [OP] New Member

    Joined:
    Jan 24, 2023
    Member:
    #416288
    Messages:
    2
    First Name:
    Jordan
    Vehicle:
    2002 silver tacoma pre runner 2.4L
    Spacers and exhaust
    There’s not I have it welded
     
  4. Jan 26, 2023 at 5:22 PM
    #4
    02hilux

    02hilux Don't follow me, I'm lost myself

    Joined:
    Sep 14, 2016
    Member:
    #197244
    Messages:
    3,773
    Planet: EARTH
    Vehicle:
    Point & Go
    So it's welded from the manifold to the exhaust tip? Even a minor leak from the oxygen sensor can trigger a p0420 and cause cat monitor to be not ready.
     
  5. Jan 27, 2023 at 12:37 PM
    #5
    Currygoat

    Currygoat Well-Known Member

    Joined:
    May 8, 2017
    Member:
    #218518
    Messages:
    309
    Bay Area, California
    Vehicle:
    2002 Tacoma 2.4 5 Speed
    Rims, 4600 Bilsteins, K&N filter
    Its my understanding that Toyota OEM O2 sensors were (are) produced by Denso. So they are the same except for branded packaging. If you have replaced both sensors (DENSO/OEM), 1st cat (OEM) and second cat (magnaflow), cleared the codes and still getting a code... I would investigate the following:

    • A malfunctioning catalytic converter is the usual suspect for a P0420 code (Magnaflow)
    • Damage to or leakage from the exhaust manifold
    • Damage or leaking in the exhaust pipe (or gaskets or O2 sensors)
    • A malfunctioning oxygen sensor in the back or front
    • Damage to the oxygen wiring
    • The O2 wiring has a loose connection

    I have the same year, color, engine and ended up replacing my entire exhaust system and 02 sensors after my header cracked, gaskets leaked and muffler rotted out. Its easy to do yourself. I replaced everything (including cats) with OEM and it was expensive as hell ($3K). Tacoma's are picky with air/fuel/exhaust/electronics parts. Many posts on here start with "I used an aftermarket rockauto sensor but im still getting a code".

    https://www.way.com/blog/p0420-code-what-it-is-and-how-to-fix-it/#:~:text=What is a P0420 code,difficult to diagnose at times.

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    Last edited: Jan 27, 2023 at 12:45 PM
  6. Jan 27, 2023 at 2:14 PM
    #6
    1schoir

    1schoir Well-Known Member

    Joined:
    Jun 7, 2021
    Member:
    #367923
    Messages:
    65
    Gender:
    Male
    Freeport, NY
    Vehicle:
    1995 Blue Tacoma Extra Cab 4 cyl 5 speed...2006 Red Tacoma SR5 Access Cab 5 speed
    Remove your Idle Air Control Valve and clean it thoroughly with carb cleaner and a proper brush. If it's "almost always had that", the cleaning may rectify that situation and give you a solid idle.
     

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