1. The site is migrating to a new server this week, so there will likely be some downtime during that process. You can follow along here for updates.

P0420 reading

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by mdoprius, Apr 26, 2021.

  1. mdoprius

    mdoprius New Member

    Joined:
    Apr 26, 2021
    7
    1
    0
    Location:
    Virginia
    Vehicle:
    2004 Prius
    Model:
    ----USA----
    01EEFAC3-0F42-4BE4-9936-25F92FCEB7A8.png Check engine light came on for the first time since I bought the car. P0420: Catalytic Converter code. I’m wondering if it could be anything else.

    Probably unrelated, but I spilled a fair amount of oil onto the engine last week. I mopped it up as best I could. That couldn’t have affected anything, could it?

    Could an old 12V be the culprit?

    How often do the sensors go bad and pop that code?

    I am reading with a fixassist 3020 from innova because it is what I could get today.

    Not sure if anyone here can make sense of any of those readings, but figured I’d give it a shot.

    Thanks for your time.
     

    Attached Files:

  2. SFO

    SFO Senior Member

    Joined:
    Feb 7, 2017
    5,245
    4,213
    0
    Location:
    Northern California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Welcome to PriusChat!!
    The sensors are usually good for around 150k or so, how many miles are on the vehicle?

    Does the vehicle burn or consume engine oil between changes?

    Once I was able to keep a P0420 at bay by replacing the upstream A/F sensor, it lasted 800 miles until I filled up with 85 gas. Lesson learned.

    Just swap in a new cat for $120 and you should be good to go, be sure to save and sell the old cat for serious profit $$$$.

    You could do it the other way around and try the A/F sensor first, then replace the cat if it tosses the P0420 again.
     
  3. mdoprius

    mdoprius New Member

    Joined:
    Apr 26, 2021
    7
    1
    0
    Location:
    Virginia
    Vehicle:
    2004 Prius
    Model:
    ----USA----
    It’s got 265k or so on it. Not sure if the sensors were ever replaced, but doubtful. That was my first thought. The feller I bought it from never got the MFD board 60 pin connector reflowed, so I assumed he didn’t do much else DIY repair. The maintenance reports he gave to me never mentioned it I don’t believe. So you think it is a better idea to replace a sensor first and see what happens?
     
  4. mdoprius

    mdoprius New Member

    Joined:
    Apr 26, 2021
    7
    1
    0
    Location:
    Virginia
    Vehicle:
    2004 Prius
    Model:
    ----USA----
    I feel like it definitely consumes engine oil between changes to some degree, but I haven’t actually measured the amount. Will do next change. I usually go for 4-5k miles on full synthetic before changing.
     
  5. SFO

    SFO Senior Member

    Joined:
    Feb 7, 2017
    5,245
    4,213
    0
    Location:
    Northern California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Check for dealer maintenance by running the VIN at : Track Your Service Records with Your Toyota Owners Account

    The upstream sensor and an aftermarket cat cost about the same, the sensor is a quicker swap. Both will likely need changing at 265k.
    Higher RPMs and spirited driving may contribute to excess oil consumption. Sounds like a decent change interval.
     
  6. mdoprius

    mdoprius New Member

    Joined:
    Apr 26, 2021
    7
    1
    0
    Location:
    Virginia
    Vehicle:
    2004 Prius
    Model:
    ----USA----
    I got some live readings, and was wondering if this looks off: the a/f sensor is staying way below what the “normal” range is (3.0-3.35 volts) and rarely goes about 1.0v. It doesn’t fluctuate much and the downstream oxygen sensor fluctuates quite a bit and stays high, over .55 volts. Is there something wrong with my A/F sensor you think?
     

    Attached Files:

    SFO likes this.
  7. mr_guy_mann

    mr_guy_mann Senior Member

    Joined:
    Sep 3, 2020
    2,873
    1,167
    0
    Location:
    NJ-USA
    Vehicle:
    2006 Prius
    Model:
    Four
    I don't know what app or scantool you are using- I am not sure I would trust it. Toyota has the upstream air fuel sensor output displayed as a voltage (even though it's actually a very small current flow). 3.3V is 14.7 : 1 ("stiochiometric") and it goes down towards around 2V when it's richer, and goes up when lean (5V on decel fuel cut). So at idle 3.3V +/- 0.2V is normal on an "enhanced" Toyota capable scanner.

    Your pics seem to show an app that's trying to display data as "generic OBD2" - which sometimes tries to "shove" enhanced data (such as A/F sensor voltage) into a 0-1V format. It doesn't always work properly. If the A/F sensor was actually that low (rich), then it should set codes for it.

    Same thing goes for the downstream S2 sensor. I don't know if your capture has valid data or not- if one or more things are suspect, then I would have to verify everything before I would trust it. You could go chasing your tail down a rabbit hole if you have bad data. That said, your S2 sensor readings are high. On a typical car I see something around 0.7V - ish on a hot engine and cat. IF S2 stays high (0.8-. 9V or more) AND fuel trims are high (+10% total or more) THEN I would look closely and likely replace the A/F sensor.

    Posted via the PriusChat mobile app.
     
  8. mdoprius

    mdoprius New Member

    Joined:
    Apr 26, 2021
    7
    1
    0
    Location:
    Virginia
    Vehicle:
    2004 Prius
    Model:
    ----USA----
    I’m using fixd, and it specifically says “a/f sensor” for the reading, not oxygen sensor 1 or any other misnomer for the part. I drove on the highway for 20 minutes to get those numbers, but very little about the a/f sensor readings changed during that time. Here and there would be a jump but it stayed pretty close to 1v. I haven’t checked fuel trims yet. There is literally nothing coming out of my exhaust that is visible whatsoever. It doesn’t smell any different in any way (don’t worry, I’m not sticking my mouth on the tailpipe). I’ll check fuel trims and post what I find.
     
  9. mdoprius

    mdoprius New Member

    Joined:
    Apr 26, 2021
    7
    1
    0
    Location:
    Virginia
    Vehicle:
    2004 Prius
    Model:
    ----USA----
    What’s funny is catalytic converter tests all pass. But I am getting p0420 error. And that is the only thing that fails the emissions test. It came on and went away and is back on again. SOMETHING isn’t right. I wouldn’t be surprised if it was cat, but I’m not some rich guy who wants to throw 2k at a guess (I drive a gen 2 prius), you know?
     
  10. mdoprius

    mdoprius New Member

    Joined:
    Apr 26, 2021
    7
    1
    0
    Location:
    Virginia
    Vehicle:
    2004 Prius
    Model:
    ----USA----
    OH, you are probably looking at the original images I uploaded. That tool was from autoZone and was incapable of providing live results. I got a new scanner and uploaded screenshots of the live feed. I have videos of it but I’m not sure if I can post them because they are long.
     
Loading...