O2 and air/fuel ratio sensors

Discussion in 'Toyota Prius Service Bulletins - TSBs' started by nadams, Mar 3, 2010.

  1. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Re: O2 and air/fuel ratio sensors.

    My post #13 shows the possible suspects. The A/F ratio sensor is the most likely failed part since you successfully measured DC and AC voltages which implies the wiring harness, the relay and ECM are OK.

    Hence if this were my car I would feel comfortable replacing the A/F ratio sensor. You'll need to decide what you wish to do, and accept responsibility for that decision.

    You asked why the A/F ratio sensor would fail. Who knows.

    Since your car logged the DTC, something is wrong. Why would any of the items on the suspect list have a problem after only 20K miles of use?

    Why did the car sit unused for two years? Had this car been in an accident?
     
  2. seilerts

    seilerts Battery Curmudgeon

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    You could try the Bosch 15624, an OEM fitment for $53 (!!!!), available from Amazon. Seems like a no-brainer
     
  3. ccdisce

    ccdisce Active Member

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    I agree O2 sensors should last a long time. The high cost of the version used on the Prii could be because it may be a WB Type.
    They come to a premature EOL when a fault causes liquid coolant hits the ceramic portion, also driving thru deep water is not good.
    It's ill-advised to puncture the PTFE insulation to Back Probe the sensor pair as atmospheric O2 will travel up the space between the strands of wire and destroy the O2 differential at the sensing element.
    Good Luck.
     
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  4. prius4ed

    prius4ed Member

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    Re: O2 and air/fuel ratio sensors.

    Hi Patrick, you raised a good point - at 20k miles it's hard to believe any of those items would go bad. Point well taken.

    Of course, I will take full responsibility for whatever happens. I didn't mean to imply that if you bet on it being the sensor and it wasn't the sensor that you'd owe me for the cost of the sensor. That would be ridiculous and immature. What I meant was if it was your car would you risk $142 on a new sensor and I believe you answered that you would.

    I'm tempted on the Bosch replacement. I don't mean to start a controversy, but I've heard Bosch ones can be problematic. I'll search the forum and internet for that Bosch unit and make up my own mind.

    Lastly, can someone educate me on how the voltage to the AFR sensor heater wires is both a measurable DC and AC voltage (but different values)? I'm a Mechanical Engineer, and that boggles my mind.

    Does anyone know if my heater voltage measured values are reasonable?

    Thanks everyone!
     
  5. direstraits71

    direstraits71 Member

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    Re: O2 and air/fuel ratio sensors.

    What was the condition of the traction battery and did it need to be recharged after 2 years? If not that's amazing retention of charge/power if the car was off all that time. I assume you needed to jump or replace the 12 volt battery?

    You really need to look at the voltage with an oscilloscope to see what's really going into the heater element.
     
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Re: O2 and air/fuel ratio sensors.

    As pointed out, if you used an oscilloscope to look at the heater voltage you would probably see that it has a DC component as well as an AC component. This is consistent with the technical repair documentation which indicates the signal is pulse-width modulated.

    Imagine an AC square wave signal superimposed upon a DC voltage. That is probably what you are measuring.
     
  7. prius4ed

    prius4ed Member

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    Re: O2 and air/fuel ratio sensors.

    Sorry guys, I don't have a scope and I don't have one to borrow. Can I use my FLUKE ET88DMM "AUTOMOTIVE METER"? The DMM manual says the meter can measure voltages on an O2 sensor (min, max and avg voltages) by using a recording feature. You ground the - wire of the DMM and the + wire connects to the O2 sensor signal wire.

    I anxiously await your suggestions.
     
  8. prius4ed

    prius4ed Member

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    Re: O2 and air/fuel ratio sensors.

    Aux battery was dead, and I replaced it with a new one. Traction battery was weak enough that the electronics wouldn't let the ICE start. I had to replace it. As soon as I did that, it fired up and drove perfectly.

    This proves gas in the bladder tank can last 2+ years and still run the car.
     
  9. seilerts

    seilerts Battery Curmudgeon

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    If the Fluke manual says it should just work, it will.

    If you still have the old traction battery, we should talk.

    I'd be willing to loan you my grinding project O2 socket, if that is what is holding you back from replacing this one.
     
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  10. prius4ed

    prius4ed Member

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    I bought the Bosch "OEM replacement" AFR sensor from Amazon and it just arrived. It has no "collar" around the hex. Anyone know if it's the right sensor?

    I'd be very interested in borrowing your socket, if we can find a cost effective way to ship it to me (zip 92603, SoCal) and back to you.
     
  11. prius4ed

    prius4ed Member

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    PS - my email is [email protected]
     
  12. Keyslammer

    Keyslammer Junior Member

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    Can you tell me where you found this? This disagrees with the current range that is supposed to be acceptable to the ECM which was posted as >0.8A and <10A.

    Thanks.
     
  13. FantasticalMagicOne

    FantasticalMagicOne Active Member

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    Didn't realize old this post was, making my original response irrelevant.
     
    #33 FantasticalMagicOne, Feb 19, 2019
    Last edited: Feb 19, 2019
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