P0031 code on '05 Prius. Also knocking sound from the engine

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by dhman2006, Jul 30, 2018.

  1. dhman2006

    dhman2006 Member

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    I have the P0031 code and from what I've found points to the A/F ratio sensor Bank 1 Sensor 1. Is this something I could do myself or is this a job left to the dealer due to the location of the sensor not being very accessible? Would I need special tools? The dealer wants $932 to fix this issue. Can I get this done somewhere else if I buy the part?

    Also, hearing some sort of knocking sound when the car starts up/ engine idles. Initially I thought the water pump was making the noise, but I don't think it is the water pump. What else should I be checking?
     
  2. bisco

    bisco cookie crumbler

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    how many miles on her, how long do you want to keep her, sand how much money are you willing to pour in?
     
  3. dhman2006

    dhman2006 Member

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    I've got about 111K miles on her. I'm trying not to spend too much money. If it ends up costing too much I'll probably trade in for a Gen3 (2011/2012)
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Did he give his opinion as to what the issue was, along with that quote?
     
  5. bisco

    bisco cookie crumbler

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    i'm just thinking you've got a potentially big problem with the knocking, and how much longer before you need a new battery?
     
  6. dhman2006

    dhman2006 Member

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    Are you referring to the 12V battery or the hybrid battery?
     
  7. dhman2006

    dhman2006 Member

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    He just said the exhaust system and the O2 sensor have problems and need to be replaced.
     
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  8. bisco

    bisco cookie crumbler

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    hybrid battery. 13 years old with low miles is a recipe for disaster.
     
  9. dhman2006

    dhman2006 Member

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    Sounds like I'm probably better off trading it in for a Gen 3. Why is low mileage with high age a bad thing? I'd think that's a good thing since it's saving life on the battery
     
  10. bisco

    bisco cookie crumbler

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    nimh batteries like to be used. taxi's do very well, sometimes lasting 3, 4, 500,000 miles.

    when they sit, they actually degrade faster. i don't understand the chemistry, but we see it a lot here.
     
  11. bisco

    bisco cookie crumbler

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    on the other hand, you put in a new $2,500. battery, and your 2005 may last you a long time.

    gen 3 has its own set of issues.:unsure:
     
  12. dhman2006

    dhman2006 Member

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    So is the car junk now or what can I do to take care of this P0031 issue now (other than forking out the $900+ that the dealer wants). One of my coworkers said the spark plugs should be changed out to see if I can take care of the knocking issue. I'm not even sure if it's knocking. I'll take a video when I go home this afternoon
     
  13. bisco

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    spark plugs at 120k, but now won't hurt. i can't help you with the sensor issue, but hopefully someone will come along who can.
    i would not say the car is a piece of junk, it is hardly broken in.:)
     
  14. Patrick Wong

    Patrick Wong DIY Enthusiast

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    It is true that DTC P0031 points to a problem with the air/fuel ratio sensor heater circuit. The problem could be in the wiring, or the sensor, or the EFI M relay, or the engine ECU.

    As to whether you can do this yourself, if you feel comfortable removing the inverter for access, then you could get to the A/F ratio sensor. As to special tools, you would need an appropriate socket to remove the sensor once you have access.

    As to whether you can get this done somewhere else, if you have an independent who specializes in Toyota hybrid service, that would be a reasonable possibility.

    Knocking sound: you need to decide whether this is a valve train sound, or a crankshaft bearing sound, etc. What happens when you place the engine under load by accelerating uphill? Is the sound still present?
     
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  15. johnjohnchu

    johnjohnchu Member

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    You can definitely replace the air/fuel ratio sensor yourself if necessary. Removal of inverter is not necessary unless you have a real big hand. May need to loosen and slide inverter coolant reservoir to the side a little to gain access from the top. Sensor socket set is available at Harbor Freight.
     
  16. dhman2006

    dhman2006 Member

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    Sorry folks, couldn't figure out how to upload a MP4 here, but I was too stupid to see the warning that Priuschat doesn't allow mp4 on my phone screen. Anyway, I've recorded a copy of the "knocking" sound that I'm hearing here --- Box

    If someone happens to know what might be causing this issue, please do let me know.

    I don't think the water pump is causing the sound. The waterpump was replaced about 5/6 years ago.
     
  17. dhman2006

    dhman2006 Member

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    Is there a manual or video that you can think of that shows how to replace the AF sensor?
     
  18. johnjohnchu

    johnjohnchu Member

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    The detail info is available in the Toyota tech manual. However, the manual had too many unnecessary steps. I did it a few years back. Actually there was no need to remove inverter. Hence hybrid system was left untouched. I did have to remove windshield wiper system to gain access from the top. Please review the following thread:

    air/fuel ratio sensor connector location? | PriusChat

    Used one of the sockets in a set from Harbor Freight:

    Oxygen Sensor and Diesel Injection Socket Set

    The other single piece Oxygen sensor socket, also available from Harbor Freight, will not fit.​
     
    #19 johnjohnchu, Aug 1, 2018
    Last edited: Aug 1, 2018
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