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Air/Fuel Sensor Deterioration #5043842 03/15/19 12:25 PM
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The Critic Offline OP
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The guy I work with is trying to convince me to replace the air/fuel sensor on my Prius due to mileage. In his opinion (he is also tunes performance cars), older air/fuel sensors have a slower response time and therefore, a new sensor should help improve the computer's ability to make more accurate fuel corrections.

The car in question has 185K and I have not noticed a sharp decline in fuel economy or driveability.

Thoughts?


2011 Toyota Prius 1.8L - 199K - Pennzoil Platinum 0W-20
2007 Honda Accord 2.4L - 140K - Valvoline Premium Blue Restore 10W-30
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5043857 03/15/19 12:42 PM
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Chris Meutsch Offline
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What is his evidence based on? Scientific numbers that he can show you?


2005 Honda CR-V EX, 278k
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5043885 03/15/19 01:09 PM
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Quest Offline
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not aware of this being a significant issue.

Fact: most OBD-II systems with wideband upstream O2 sensors, their ECU has built-in tests to report both upstream and downstream O2 sensor issues, including "lazy" sensors (esp. upstream one which is wideband and heated also)....I had dealt with (incl. wifey's camry) upper sensor reaching the test "threshold" by ECU and had to be replaced to restore proper functionality.


"Internet discussion boards act as echo chambers for conspiracy dittoheads" A.Allen
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5043934 03/15/19 01:52 PM
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mclasser Offline
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Hook up a scanner and see what the fuel trims and sensor voltages look like.


2018 Hyundai Elantra VE
2013 Honda Pilot EX-L 4WD
2002 Honda Accord EX-L

Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5043943 03/15/19 01:58 PM
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StevieC Offline
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No light or driveability problems leave it alone.


'18 Caravan - 45k KM - AMSOIL SS 0w20, Fram Ultra, TC-W3 500:1
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Re: Air/Fuel Sensor Deterioration [Re: Quest] #5043996 03/15/19 02:40 PM
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The Critic Offline OP
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Originally Posted by Quest
not aware of this being a significant issue. Fact: most OBD-II systems with wideband upstream O2 sensors, their ECU has built-in tests to report both upstream and downstream O2 sensor issues, including "lazy" sensors (esp. upstream one which is wideband and heated also)....I had dealt with (incl. wifey's camry) upper sensor reaching the test "threshold" by ECU and had to be replaced to restore proper functionality.

I think my friend's theory is that the "thresholds" are quite significantly, so even if the system does not trigger a fault, there is still room for improvement.

Originally Posted by mclasser
Hook up a scanner and see what the fuel trims and sensor voltages look like.

That won't tell you anything useful, at least not for this specific purpose.


2011 Toyota Prius 1.8L - 199K - Pennzoil Platinum 0W-20
2007 Honda Accord 2.4L - 140K - Valvoline Premium Blue Restore 10W-30
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044050 03/15/19 03:18 PM
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eljefino Offline
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Mine has 270k and works fine. smile

Watching it in Torque is fun; above 50 MPH when I coast the engine keeps running but at an 18:1 AFR instead of 14.7.

When the gas motor kicks on and off there's the tiniest surge in AFR but it settles and locks in very quickly.

This is of course the computer's opinion of what's going on. My 2nd gen prii are slightly "bumpy" kicking in and out, particularly when warming up, but apparently normal by design.

Re: Air/Fuel Sensor Deterioration [Re: mclasser] #5044076 03/15/19 03:38 PM
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gathermewool Offline
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Originally Posted by mclasser
Hook up a scanner and see what the fuel trims and sensor voltages look like.


That would be assuming the MAF is reading correctly.

I would compare fuel trims before and after cleaning the MAF.


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Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044077 03/15/19 03:41 PM
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bdcardinal Online Content
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I might have done it when the head gasket was replaced on the off chance coolant contaminated the sensor.


2014 Ford Mustang GT Track Pack
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Opinions expressed are my own.
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044085 03/15/19 03:50 PM
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Skippy722 Offline
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I’ve heard it’s recommended to replace them at 100k, but you can easily go much further.

Replaced the oxygen sensor in my Caliber last year... no matter how I drove it got a constant 20-22mpg, calculated by hand. New sensor got me 25-27.


2016 Chrysler 300S v6
2018 Dodge Grand Caravan GT

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Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044163 03/15/19 04:31 PM
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JamesBond Offline
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I replaced the original afr sensor in my 04 civic last year because the heater wasn’t working. I drove it for almost a year with the bad sensor then changed it for a denso sensor. The car always ran the same and the mpg never changed. If we didn’t have state inspections where I live I wouldn’t have changed it.

Re: Air/Fuel Sensor Deterioration [Re: bdcardinal] #5044251 03/15/19 05:21 PM
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The Critic Offline OP
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Originally Posted by bdcardinal
I might have done it when the head gasket was replaced on the off chance coolant contaminated the sensor.

I forgot to mention that. Good point.

Apparently, BMW recommends replacing Oxygen Sensors every 120K or 150K depending on the vehicle. I have heard this before and I thought it was a rumor, but apparently it is true. Take a look at the snapshot from the maintenance manual below - it was taken from the manual of a 2015 BMW 3-series. Very interesting...

BMW.PNG
Last edited by The Critic; 03/15/19 05:22 PM.

2011 Toyota Prius 1.8L - 199K - Pennzoil Platinum 0W-20
2007 Honda Accord 2.4L - 140K - Valvoline Premium Blue Restore 10W-30
Re: Air/Fuel Sensor Deterioration [Re: gathermewool] #5044276 03/15/19 05:43 PM
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The Critic Offline OP
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Originally Posted by gathermewool
Originally Posted by mclasser
Hook up a scanner and see what the fuel trims and sensor voltages look like.


That would be assuming the MAF is reading correctly.

I would compare fuel trims before and after cleaning the MAF.

MAF was replaced 35k ago due to a failure.


2011 Toyota Prius 1.8L - 199K - Pennzoil Platinum 0W-20
2007 Honda Accord 2.4L - 140K - Valvoline Premium Blue Restore 10W-30
Re: Air/Fuel Sensor Deterioration [Re: eljefino] #5044517 03/15/19 09:28 PM
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CR94 Offline
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Originally Posted by eljefino
... Watching it in Torque is fun; above 50 MPH when I coast the engine keeps running but at an 18:1 AFR instead of 14.7.

When the gas motor kicks on and off there's the tiniest surge in AFR but it settles and locks in very quickly.

This is of course the computer's opinion of what's going on. ...
Is that in a Prius? If so, are you sure that indicated 18:1 is real? Should be infinity-to-one when coasting fast enough that the engine is turning, because it shouldn't be injecting any fuel. (That's similar to fuel-cut mode while coasting in a modern non-hybrid.)


2011 Toyota Prius now at 106K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: Air/Fuel Sensor Deterioration [Re: CR94] #5044583 03/15/19 11:13 PM
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Skippy722 Offline
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Originally Posted by CR94
Originally Posted by eljefino
... Watching it in Torque is fun; above 50 MPH when I coast the engine keeps running but at an 18:1 AFR instead of 14.7.

When the gas motor kicks on and off there's the tiniest surge in AFR but it settles and locks in very quickly.

This is of course the computer's opinion of what's going on. ...
Is that in a Prius? If so, are you sure that indicated 18:1 is real? Should be infinity-to-one when coasting fast enough that the engine is turning, because it shouldn't be injecting any fuel. (That's similar to fuel-cut mode while coasting in a modern non-hybrid.)


IIRC, torque won’t go to infinity. When I would monitor it I would use the voltage graph though, it would just peg itself at the top


2016 Chrysler 300S v6
2018 Dodge Grand Caravan GT

Slight Mopar obsession
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