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Trouble Code - P0000 P0031

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by 13Plug, Feb 23, 2009.

  1. 13Plug

    13Plug Active Member

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    So here's the deal. I've got an 08 Prius, 15K km (about 9K miles), less than a year old.

    The CEL came on when I was out of town (didn't have my code reader with me). It came on the first time on a cold start. I turned the car off and on a few times and the light cleared. Next day light came on first thing in the morning and stayed on. Got home, got out my trusty ScanGauge II and looked up the code.

    P0000. Hmmm.... what's that code. So I went to

    OBD-II Check Engine Light Trouble Codes

    It seems that's not a valid code (I kinda figured). So I kept going in and out of "scanning" for codes and it told me P0000 a bunch of times but one time it gave me P0031 which is Oxygen (A/F) Sensor Heater Control Circuit Low.

    http://www.obd-codes.com/p0031

    Well the P0031 code is not a popular one. I was only able to find one good post about that code here in the forums:
    Anyway, it looks like the front (oxygen) air fuel ratio sensor is toast. I used the handy XGauge feature of the SG and watched the oxygen sensor readings. The car never goes into closed loop mode so I can't ever get a front O2 sensor reading. Oh well.

    What I'd like to do is check it myself before I take it to the dealer just to be sure. Yes, I'd like to disconnect it and take my ohmmeter and check the resistance. I know, I know, it's under warranty, blah blah :)

    Here's the problem. I don't know the pin/wire colors and what they mean because I don't have a repair/service manual. Can someone out there share with me the 4 wire colors and what each wire is what? Well I think it's 4 wires, I haven't had a chance to jack up the car and see...

    Thanks!
     
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  2. dogfriend

    dogfriend Human - Animal Hybrid

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    It looks like Red and Green are the signal wires going to the ECU, Yellow is the Heater Circuit also going to the ECU, Black is battery voltage coming from the EFI main relay.
     

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  3. dogfriend

    dogfriend Human - Animal Hybrid

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    This may help.
     

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  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi Swanny,

    It looks like the heater within the air/fuel ratio sensor has failed open. Your ohmmeter can verify this, since dogfriend provided the connector pinout and the resistance spec of 1.8 - 3.4 ohms.

    Good luck getting that part replaced under warranty.
     
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  5. 13Plug

    13Plug Active Member

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    Are you being sarcastic?
     
  6. dogfriend

    dogfriend Human - Animal Hybrid

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    I don't think Patrick meant it the way you took it.

    It should be covered under the emissions warranty, so you shouldn't have any issue getting it replaced.
     
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  7. 13Plug

    13Plug Active Member

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    Well it's too cold today to look at it myself (I don't have a heated garage) so I made an appointment for the dealer tomorrow afternoon. Thx.
     
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  8. 13Plug

    13Plug Active Member

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    Well I went to a friends house (he has a heated garage). I put it inside for maybe 20 minutes, located the sensor, but WOW is it not in an accessible location. I'll just leave it up to the dealership to replace that while it's under warranty!

    Oh, and when I left the check engine light was off. So maybe sitting in the warm garage fixed the problem? I don't know. We'll see if it comes back on again tomorrow...
     
  9. 13Plug

    13Plug Active Member

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    OK well I went out to buy some bread. The light was off and the car was in closed loop mode on the way there. When I came out and started it again it was in open loop and the CEL was on again. Oh well, it's off to the dealer tomorrow anyway...
     
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  10. Cip

    Cip Junior Member

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  11. 13Plug

    13Plug Active Member

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    The fix for my P0031 code was for Toyota to replace the front air/fuel ratio sensor. The problem never returned, and it's been three years. If you need to replace the sensor on your car, bite the bullet and pay the extra for the Toyota OEM sensor. This isn't a "regular" O2 sensor that you'd buy at the local auto parts store. Good luck.
     
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  12. Cip

    Cip Junior Member

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    OK! I replaced the AF sensor a month ago. The code seems to be gone.
     
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  13. jimm27

    jimm27 Junior Member

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    folks... I see this is an old thread, but it popped up first when I went looking for code P0000. The car is a 2008 with 55k miles. I got that code along with the triangle of death, but the car seemed to be running fine. I drove a short distance, stopped and checked the codes again. This time, it was U0100. Since I didn't have my phone with me and couldn't look the code up, I cleared it and hoped for the best. The next time I started the car, I was back to P0000. Another stop, and the triangle went away and the check engine light went away.

    Immediately before this started, just after I turned the car off, I unplugged my ScanGuage II and moved the connector to the side port. (It was still getting power when I did this.) That seems too stupid to have been the cause, but it was the last thing I did before I turned the car back on a few minutes later and got the triangle. Any ideas? Should I just be happy that it went away and leave it at that?

    (Additional info) -- The car is due for an oil change, so the maintenance light is lit. I have the feeling this might be the cause of the P0000 code, since that's a generic code.
     
    #13 jimm27, May 28, 2014
    Last edited: May 28, 2014
  14. Alan Sampson

    Alan Sampson Junior Member

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    My CEL came on and am getting codes Poo31 and P2237 from my 2010 Prius III. Seems unlikely that both O2 sensors went bad at once, so I suspect the A/F ratio sensor. Is there a better explanation? Is there a good way to diagnose? Are these covered under the emissions warranty? Can anyone suggest a decent dealership service department in the Boston area? Should I have started a new thread for this? Thanks!
     
  15. homermn

    homermn Junior Member

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  16. homermn

    homermn Junior Member

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    I have the codes P0031 and P2237 on my 2008 Prius. I'm not keen on spending $500-700 on this right now, so I'm trying to figure out what I can do on my own. I've understood some of what's on this thread. My question right now, though, is how long can I wait to fix this? I'm sure I'll realize I just have to bite the bullet and pay the money, but I want to know if this is something that will damage my Prius the longer I wait or if it makes it unsafe to drive. Thanks for any guidance.
     
  17. bisco

    bisco cookie crumbler

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    the a/f sensor will affect the engine operation and mpg's, but won't harm anything if you can live with it.
     
  18. MattLTH

    MattLTH Junior Member

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    For what it's worth, I just had P0000 pop up (along with 'check engine' and the dreaded RTD [red triangle of death]) on my 2007, and this was a day after I had my emissions tested.

    When I started my car, the idle was really low engine sounded rough. When I got it on the street, that's when all the errors popped up. I limped home on the traction battery as the ICE (internal combustion engine) had turned off. When I tried rebooting the car, the engine would idle at low RPM for about 10-seconds, then shut down.

    I checked the 12V battery, which has low voltage (11.95V) but not to the point of being the problem. After resetting the codes with my ScanGaugeII, I would occasionally get P0486 and P3190. The former is not a code I know, but the latter has a myriad of potential issues, including the MAS (mass airflow sensor.)

    Since it was easy to do, I disconnected the MAS connector, then the engine would idle at a more nominal RPM, and would not switch off after 10-seconds. This is when I got P0486. So I pulled the MAS out of the car and inspected it visually, and I noticed a chunk of something — almost like a thin vein from a dried leaf — stuck to one of the probes. I used a can of MAS cleaner to ensure all foreign matter was removed from the probes, then replaced it in the engine without using the two screws to secure it, and reconnected its cable.

    I reset the codes again and rebooted the car. That seems to have solved the problem because the engine idled at nominal speed and didn't shut off after 10-seconds. I screwed it back in and drove the car for a while and she seems like the same old girl I've known for 13-years.

    If anything changes, I'll post the results.

    MattLTH