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Air/Fuel Sensor Deterioration #5043842
03/15/19 01:25 PM
03/15/19 01:25 PM
Joined: Aug 2004
Posts: 20,885
CA
The Critic Offline OP
The Critic  Offline OP

Joined: Aug 2004
Posts: 20,885
CA
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 - 193K - Idemitsu ZEPRO Adv. Moly 0W-20
2007 Honda Accord 2.4 - 137K - Mobil 1 EP HM 5W-30
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5043857
03/15/19 01:42 PM
03/15/19 01:42 PM
Joined: Feb 2006
Posts: 2,762
Cincinnati
Chris Meutsch Offline
Chris Meutsch  Offline

Joined: Feb 2006
Posts: 2,762
Cincinnati
What is his evidence based on? Scientific numbers that he can show you?


2005 Honda CR-V EX, 273k
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5043885
03/15/19 02:09 PM
03/15/19 02:09 PM
Joined: Dec 2004
Posts: 7,403
beaver land EH?
Quest Offline
Quest  Offline

Joined: Dec 2004
Posts: 7,403
beaver land EH?
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 02:52 PM
03/15/19 02:52 PM
Joined: Apr 2013
Posts: 2,692
The Northeast
mclasser Offline
mclasser  Offline

Joined: Apr 2013
Posts: 2,692
The Northeast
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 02:58 PM
03/15/19 02:58 PM
Joined: Aug 2008
Posts: 25,014
ON, Canada eh?
StevieC Offline
StevieC  Offline

Joined: Aug 2008
Posts: 25,014
ON, Canada eh?
No light or driveability problems leave it alone.


'18 Caravan - 36k KM - AMSOIL SS 0w20, Fram Ultra, TC-W3 500:1
'06 Santa Fe - 535k KM (Retired)

There is no such thing as "lifetime" fluids! mad
Re: Air/Fuel Sensor Deterioration [Re: Quest] #5043996
03/15/19 03:40 PM
03/15/19 03:40 PM
Joined: Aug 2004
Posts: 20,885
CA
The Critic Offline OP
The Critic  Offline OP

Joined: Aug 2004
Posts: 20,885
CA
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 - 193K - Idemitsu ZEPRO Adv. Moly 0W-20
2007 Honda Accord 2.4 - 137K - Mobil 1 EP HM 5W-30
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044050
03/15/19 04:18 PM
03/15/19 04:18 PM
Joined: Jun 2003
Posts: 34,650
ME
eljefino Offline
eljefino  Offline

Joined: Jun 2003
Posts: 34,650
ME
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 04:38 PM
03/15/19 04:38 PM
Joined: Jan 2009
Posts: 7,179
New England
gathermewool Offline
gathermewool  Offline

Joined: Jan 2009
Posts: 7,179
New England
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.


'14 Forester XT FA20DIT (Cobb Stage 1)
Edge 0W-40 + FU filter (64,774 miles)
'15 Legacy FB25 (OEM Stage, uh, neg. 7?)
Magnatec 5W-20 + FU filter (47,300 miles)
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044077
03/15/19 04:41 PM
03/15/19 04:41 PM
Joined: Jun 2005
Posts: 12,816
Santa Barbara, CA
bdcardinal Offline
bdcardinal  Offline

Joined: Jun 2005
Posts: 12,816
Santa Barbara, CA
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
1995 Ford Mustang GT

Ford/Mazda Parts Counter
NRA Benefactor Member
Opinions expressed are my own.
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044085
03/15/19 04:50 PM
03/15/19 04:50 PM
Joined: Nov 2018
Posts: 1,051
Chicagoland
Skippy722 Online content
Skippy722  Online Content

Joined: Nov 2018
Posts: 1,051
Chicagoland
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

Slight Mopar obsession
Re: Air/Fuel Sensor Deterioration [Re: The Critic] #5044163
03/15/19 05:31 PM
03/15/19 05:31 PM
Joined: Dec 2006
Posts: 1,076
midwest
JamesBond Offline
JamesBond  Offline

Joined: Dec 2006
Posts: 1,076
midwest
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 06:21 PM
03/15/19 06:21 PM
Joined: Aug 2004
Posts: 20,885
CA
The Critic Offline OP
The Critic  Offline OP

Joined: Aug 2004
Posts: 20,885
CA
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 06:22 PM.

2011 Toyota Prius 1.8L - 193K - Idemitsu ZEPRO Adv. Moly 0W-20
2007 Honda Accord 2.4 - 137K - Mobil 1 EP HM 5W-30
Re: Air/Fuel Sensor Deterioration [Re: gathermewool] #5044276
03/15/19 06:43 PM
03/15/19 06:43 PM
Joined: Aug 2004
Posts: 20,885
CA
The Critic Offline OP
The Critic  Offline OP

Joined: Aug 2004
Posts: 20,885
CA
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 - 193K - Idemitsu ZEPRO Adv. Moly 0W-20
2007 Honda Accord 2.4 - 137K - Mobil 1 EP HM 5W-30
Re: Air/Fuel Sensor Deterioration [Re: eljefino] #5044517
03/15/19 10:28 PM
03/15/19 10:28 PM
Joined: Mar 2016
Posts: 2,208
Western S.C.
CR94 Offline
CR94  Offline

Joined: Mar 2016
Posts: 2,208
Western S.C.
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 101K
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
03/16/19 12:13 AM
03/16/19 12:13 AM
Joined: Nov 2018
Posts: 1,051
Chicagoland
Skippy722 Online content
Skippy722  Online Content

Joined: Nov 2018
Posts: 1,051
Chicagoland
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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