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P0420

Discussion in 'Generation 1 Prius Discussion' started by camperman, Jan 28, 2014.

  1. camperman

    camperman Junior Member

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    Have a 2003, roughly 160K.

    Just got a free replacement power steering as I got in under the extended warranty that ended 12/31.

    Dealer (#1) who did power steering warranty work said we needed new coils as a precode had shown up saying we were getting misfires. We opted to delay and now 2 months later we got a MIL. Took it to a dealer (#2) for a P0420 and they insisted we needed a new Cat; although they were equally insistant that they saw no evidence of misfires or need for coils.

    I asked what testing they did beyond the computer telling them P0420 and the answer was nil. I told them I didn't believe the CAT would fail randomly and wasn't going to drop that kind of $$ without more diagnostics on upstream power train so decided to take the car home as I have another 1.5 years until I need emissions again.

    The P0420 hasn't come back since clearing the code 150 miles or so ago. However any thoughts on the O2 readings I got tonight, thinking about replacing the sensors. I have been monitoring the O2 performance and besides the voltage on the downstream sensor seeming to wander a bit, I captured about 2 minutes where the two sensors fell into line which I don't quite understand. These readings were started after about 15minutes of full speed highway driving and the first 80% are around 60mph with the last 20% of readings as we slowed down to get off the highway around 40mph.
    O2 Sensor Voltage.gif
    Also I have the other 15 or so measurements over this same 10 minute window covered by this data if anyone has a recommendation bout anything else I should be looking at. Car was idling pretty rough upon starting but once it gets warmed up we don't notice any issues, power or otherwise.
    Load and Speed.gif
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Regarding the rough idle, when was the last time the iridium spark plugs were replaced?

    2. The B1S2 sensor, which is downstream from the catalytic converter, should show relatively constant voltage readings compared to the B1S1 sensor which should show big swings in voltage as the engine air/fuel mixture swings back and forth from rich to lean continually. The B1S2 constant readings would indicate that the catalytic converter is doing its job of changing hydrocarbons and carbon monoxide in the exhaust to water vapor and carbon dioxide. To the extent that B1S2 follows along with B1S1, that is evidence that the catalytic converter is not doing its job.
     
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I agree with Patrick although I see enough variability in the second O{2} sensor that the catalytic converter looks OK. I am a little curious about the drop out of the first O{2} sensor in the recorded data. Perhaps it is time to check the connectors?

    The O{2} sensors are critical for fuel trim. If one is intermittent, I would work to get it (or both) replaced before the more expensive catalytic converter exchange. One 'shade tree' mechanic trick is to swap the O{2} sensors, front and back. This not only reseats the connectors but also gives a chance to check their external appearance.

    One thing I would be interested in would be any carbon on the front sensor. This would suggest mixture has been running rich.

    Bob Wilson
     
  4. camperman

    camperman Junior Member

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    On Spark Plugs, I will track that down, its been at least a couple years.

    On O2 sensors ya if the cat wasn't absorbing anything I was expecting them to mirror each other, just not intermittently in relatively stable driving conditions at ~60mph. I will plan this weekend to try what you are suggesting and make a visual inspection of the front sensor and try swapping them.

    In terms of fuel trim, the data pulled over that same drive time is as follows; and I am a novice, but I thought LTFT was essentially a moving average of STFT, so I was a bit surprised STFT was sitting around 0 while LTFT is sitting solidly on the positive side.
    Fuel Trim.gif
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    If you are going to the trouble of removing the B1S1 sensor, I suggest that you actually replace it with a correct new Toyota part (not some generic). The reason for my suggestion is that if you are lucky, you may find that replacing B1S1 will allow the catalytic converter to continue to function sufficiently well enough so that DTC P0420 will go away.

    The engine ECU depends upon B1S1 to provide feedback regarding air/fuel mixture so that the ECU knows when to swing between a rich mixture and lean. If B1S1 is marginal, the ECU will take longer to move from rich to lean, which results in more emissions being produced and therefore more work for the catalytic converter.

    For the same reason, if the spark plugs are marginal, then they should be replaced with the correct iridium NGK or Denso plugs (as specified in the owner's manual.) The spark igniters should be cleaned and examined for damage such as burn marks, cracks, rust deposits, and corrosion on the electrical contacts. Replace if needed. If the engine is not misfiring, then there will be less HC being produced which needs to be catalyzed.

    While you are at it, look at the engine air filter and replace it if you cannot see light passing through when holding the filter up to the sun.
     
  6. tnt01prius

    tnt01prius Member

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    Has anybody actually replaced the upstream O2 sensor on the NHW11? Can it be done w/o removing the inverter to gain access to the connector? As it is, it will cost me $175. plus shop fees, plus part at the dealer.
    BTW, is the Denso after market O2 on ebay the same as the OEM? It comes pkgd in the Denso box with the same part number from Toyota parts online and cost only $36-52. shipped.
     
  7. kutcht1

    kutcht1 Member

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    The sensor numbers are:
    234-4624 upstream
    234-4623 downstream
    The denso you found should be OEM. I think the inverter does not have to be touched but the sensor can be accessed by removing the wiper cowl to gain enough room. I also want to get mine changed.
    TomK
     
  8. tnt01prius

    tnt01prius Member

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    You're correct. I was able to remove the upstream O2 sensor after removing the wiper cowl. I also removed the throttle cable bracket (in the way) and the exhaust manifold heat shield (moved it slightly away from the sensor) to be able to get a crows foot socket on the sensor. Please note that this is still a very tight access. I'm awaiting a new sensor.
     
  9. kutcht1

    kutcht1 Member

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    Be sure to let us know your outcome as I am interested. I also have a P0420 code that come on about once every week and stays for four or five days. Already bought the upstream sensor but need a spare day to tear into it since I am sure everything will not go smoothly. I bought the Denso 234-4624 sensor.
    TomK
     
  10. tnt01prius

    tnt01prius Member

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    The chain parts stores and some online Toyota parts stores indicated the 234-4623 was for both applications, hence my original question. I also ordered a new Denso 234-4624 from Pyramid Auto Parts on ebay at very discounted prices.

    Note: Recommend dousing any rusty bolts and the base of old sensor with Zep 45 or other nut buster a couple of times and let it sit for a while to try and avoid breaking off bolt heads. If there is an O2 sensor socket available, you may not have to move the manifold heat shield. This is also a good time to clean things up and treat any surface rust on parts (no thanks to road salts), and to change the spark plugs if it's close to that time. I removed the K&N air filter after 9 years. I'm now recommending quality OE type filters as a precaution to keep air clean and more oil free in the intake/emissions downstream.

    I'll come back if there is any thing to report after installing new sensor.
    100_7340.JPG 100_7339.JPG 100_7338.JPG 100_7345.JPG
     
    bwilson4web likes this.
  11. tnt01prius

    tnt01prius Member

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    Upstream O2 sensor installation went well. P0420 returned after a few trips. Next step - replace the cat.
     
  12. kutcht1

    kutcht1 Member

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    Is it worth it to replace the cat? I have a very similar situation as my CE light goes off and on with only the Po420 code. With the likelyhood of a major repair in the future spending for a replacement cat unless you have to pass emissions does not seem money well spent. With the temps now above 50 every day my 2002 Prius with 150,000 miles in now getting above 45 mpg. I will be doing the upstream O2 sensor like you and hope for the best but not hold my breath. If it comes back drive it like it is.
    TomK
     
  13. tnt01prius

    tnt01prius Member

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    I think we share the same philosophy. Even if the cat is not at peak performance, the Prius is still low emissions. However, I've moved to the smoggy Valley of the Sun in AZ and a missions test is required.

    Aftermarket cat is $77. with s.h. and $200. to weld/install. An OEM front pipe assembly is $1000. + online. My current financial situation says install the aftermarket cat and hope the bypass valve holds up.
     
  14. kevin3

    kevin3 Junior Member

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    Any Idea if this will work on a Gen2 with the heat shield welded? I had it welded because it was loose and bolts were not tightening it. I thought it was the noise but now that it's tight it still has rattle noise when i'm on the throttle... probably backed up exhaust or leaking gasket. I have the 138 and 0420 codes (O2 sensor/cat) and I have a salvaged upper and lower 02 Sensors and full cat/tailpipe I need to install. Shop said It needs to remove manifold to replace the upper sensor (3+ hours)
     
  15. tnt01prius

    tnt01prius Member

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    [/QUOTE]Any Idea if this will work on a Gen2 with the heat shield welded? I had it welded because it was loose and bolts were not tightening it. I thought it was the noise but now that it's tight it still has rattle noise when i'm on the throttle... probably backed up exhaust or leaking gasket. I have the 138 and 0420 codes (O2 sensor/cat) and I have a salvaged upper and lower 02 Sensors and full cat/tailpipe I need to install. Shop said It needs to remove manifold to replace the upper sensor (3+ hours)[/QUOTE]

    I also own a 2005, but haven't tried replacing it's air/fuel ratio sensor. If you're removing the exhaust, then yes it may require removing the manifold to replace this sensor. If you're only replacing this sensor: my Bentley Repair Manual states that the inverter must be removed, which involves draining the coolant and removing high voltage power cables too. However, just removing the cowl may provide enough access - perhaps you can find someone here who has done it.

    I don't recommend a salvaged cat or sensors. I found both OEM sensors for about $87. on ebay, so to me it made sense to go with new sensors while I'm in there. As for the cat, my salvage cat was indicating inefficiency, therefore it didn't get rid of the 0420. I purchased a new aftermarket cat for $77. shipped and had it welded and installed for $67.

    Finally, replacing these emissions parts does not necessarily alleviate the root cause why these parts went bad in the first place. There are a whole host of causes why a cat and/or sensors are ruined. Having ignored emissions related DTCs in the past seems to be a main cause to ruining these parts. A good tech could help you find any deficiencies in the emissions system.