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Discussion Starter #1
Fellow members,
Can some please post some normal voltage readings for the pre cat. AF oxygen sensors (S1) as well as the post cat sensors S2)
Bank 1 = firewall side
Bank 2 = front of engine
At 2500rpm I am getting 3.1 V to 3.2 V , on both S1 (B1S1 , B2S1) pre cat
At 2500rpm.... on B1S2 .5-.7 V and on B2S2 .09-.27 V post cat
These are the values from my scanner
 

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from my experience, those reading is pretty much useless without correlate to other outputs together.

last year my 06 sienna got p0430, and then p0420, and ended up spent about $300 buying 4 aftermarket denso sensors from rockauto to address my check engine light.

i ran the engine to normal operating temperature, and when watched AF sensor and O2 sensor reading together for each bank, and the voltage reading will vary inversely to each other
for example, af range from 2.0v to 3.99v, and o2 range from 0.0 to 0.9v,
at idle af should read around 3.3v and o2 should read at 0.7v.

as engine rev up or down, o2 voltage should followed to changes in af inversely and instantaneously
a rich and lean condition can be simulated, and 02 reading will either go min or max depend the air fuel mix ratio condition.

the cause of my check engine light, my o2 sensor reading was 3 or 5 seconds delayed in response to the changes in AF.

eric from south main auto give one of the best diagnose on toyota a/f from this youtube video

 

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yes, after changing all 4 sensor, the check engine light p0430 and p0420 has not came back on once for almost a year now.
and i did noticed immediate increased fuel economy after changing, used to get 330 to 350 DTE, now gotten to 370 to 400 on my overhead console.

that code could have been caused by many things, ranging from loose gas cap, clogged pvc valve, bad sensors, and bad cats.
in my case, i took immediate action as soon as the light came on to avoid further damage (if any) to my cat.
based on my vehicle sensor voltage readings, as well as the mileage (about 160k miles ), i leaned more toward my sensor going bad.
 

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Discussion Starter #5
I looked at the freeze frame data and the fuel trim (long term ) was like 25. I changed out two hoses, one from the intake resonator to the valve cover as it had a crack and also the pcv hose ( hard and brittle) I installed two new post cat oxygen sensors and so far no check engine light . Hoping this was the fix .
 

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Not sure if you also look at the pcv valve, a year ago I removed it and cleaned with brake cleaner, last week I replaced with a brand new $5 pcv from stealership. I can feel my van run smoother. Though the old pcv valve still rattled when I shook it, but not as loud as the brand new one, but again rattle may not indicate fully working.
 

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Discussion Starter #7
In hindsight , I should have changed the pcv valve as it has been 5 years since I renewed it (50k on it) I will do it this weekend. Thanks for mentioning it.
 
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