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Nonstop P0430 Check Engine Light

Discussion in '2nd Gen. Tacomas (2005-2015)' started by socaloctacoma, Nov 25, 2024.

  1. Nov 25, 2024 at 3:57 PM
    #1
    socaloctacoma

    socaloctacoma [OP] Active Member

    Joined:
    Dec 14, 2019
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    First Name:
    Tanner
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    2008 TACOMA
    Hello all,

    My check engine light comes on with a P0430 code. When I replace the o2 sensor and reset the computer it goes away for about 300 miles and comes back on.

    I had to smog my truck 2 weeks ago and bought another denso 234-4261 sensor, got it to pass smog, and check engine light came back on after 386 miles.

    This has been going on for about 2 years and I just leave the check engine light on the whole time.

    Do you think it could be my cat?
     
  2. Nov 25, 2024 at 4:14 PM
    #2
    Dm93

    Dm93 Test Don't Guess

    Joined:
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    2014 DC OR 6spd 4x4
    Predator tube steps, Ranch Hand grill guard, Magnaflow CatBack exhaust, Toyota tool box & bed mat, 2LO Module by @Up2NoGood, Rearview Compass/Temp Mirror, Tune by @JustDSM.
    It's very rare that I see an AFR or O2 sensor as the cause for a P0420, an exhaust leak near or upstream of the AFR or O2 sensor can cause it but don't see that very often either. Most of the time it's a catalyst that is no longer functioning properly.

    To understand why the code is setting you have to understand how the PCM monitors catalyst efficiency and the voltage thresholds for an O2 sensor.
    Because a normally functioning converter stores oxygen this allows the PCM to monitor their function using the AFR and O2 sensor.

    There are 2 methods used to monitor the catalytic converter function:

    Downstream O2 switch rate: The PCM compares the rich/lean switch rate of the upstream and downstream sensors under certain driving conditions. (older vehicles for the most part used this method and were relatively easy to "fool" with various methods)

    Oxygen storage capacity: The PCM will deliberately force the air/fuel ratio to a rich or lean state under certain driving conditions and measure the length of time between when the upstream sensor switches and when the downstream sensor switches. (almost all modern vehicles use this method or a combination of both methods and are harder to "fool")


    A standard O2 sensor generates a 0-1v signal based on oxygen in the exhaust, because they have a very narrow operating window essentially anything above 0.5V (500mV) is rich (<14.7:1) and below 0.5V (500mV) is lean (>14.7:1) although usually the "dead zone" threshold for a lean/rich "switch" is around 0.45V (450mV) - 0.55V (550mV)


    The way we check converters and sensor operation with a scan tool is graphing the AFR and O2 sensor data.
    It's kinda hard to explain what good and bad data looks like as far as sensor operation but typically with a good functioning cat at operating temp the downstream sensor should stay relatively constant at around 0.7V (700mV).


    Here's some known good captures, you can see how the AFR (Upstream) sensors "switch" very rapidly and the O2 (Downstream) sensors stay relatively constant.

    First one is an accel and decel event and the 2nd is a steady cruise.

    [​IMG]


    [​IMG]
     
    sean.hwy likes this.

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