Intermittent O2 sensor code

GM Guy

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#1
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MAKE:Scion
MODEL:tC
YEAR:2009
MILES:81000
ENGINE
:2.4L
DESCRIBE ISSUE....My son's car...The cel has come on a couple times and we have previously just erased the code with a hand held code reader( oxygen sensor all previous times, downstream, I think...) NO CODES PRESENTLY. I now have Auto Enginuity software that I can connect. I can read up to 6 sensors simultaneously. My 1st question is which 6 sensors should I be watching? We went for a 10 or 15 mile drive and I chose O2 sensor voltages (S1B1, S2B2) there was a 2.5-3 volt difference between the readings. Not sure how to interpret or what to look for??
Is there a wrench that could guide me a little on the effective use of my scan software? I could use some pointers.
 
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#2
what code have you erased ? Has it been the same code?

Sorry I do not use auto equity.

pre cat is AF sensor pst cat is HO2 Sensor - B1S1 and B1S2 pretty sure NO bank 2 - BUT ONce you post code I can get info
 
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#3
How many O2 sensors does the car have? I would be watching sensor data on the graphing screens and compare sensor values during varing engine conditions.
Autoenginuity graphing...
 

GM Guy

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#5
Sorry, before tonight I have just been blowing the code away as a nusiance "O2 code". I read a Scion forum and found a bunch of knotheads' babble, called my Scion dealer about the factory warranty on the cat. The service mgr said that is 13 years of service, he'd never replaced a Toyota/Scion cat. He talked about how the a/f ratioaffects the O2 readings so it got me to thinking , maybe I ought to connect the laptop to it and watch the different sensors. I just don't know which 6 would hive me the info I need to diagnose the problem. FIRST, I know that the problem has to be present, though, It's not now.
 
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#7
2 sensors - pre cat is an AF ratio sensor... post cat is a o2 sensor...

What is the code - as far as using auto equity to graph them dan can help, BUT what code would help.

NORMAL B1S1 AF @3.0 -3.35v B1S2 o2 @.4 -.55v
 

GM Guy

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#8
Sorry, Next time it sets, I'll get the code. It has been the same code each time it has set.
We took the car for a spin tonight and the voltages I observed were in the ranges you have listed, kev2.
It has been setting once every couple of weeks. Next time, I'll have the details.
 

nickb2

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#9
My 1st question is which 6 sensors should I be watching?
RPM, ECT, long term fuel trims, short term fuel trims, B1S1 voltages, B1S2 voltages. That = 6.

Here are PDF charts you can use that only require a digital voltmeter to check your aft and post sensors. Hope they help.

Now, as said before, a code would help pinpoint a lean or rich or a heater circuit code etcetera. Does drive-ability seem to be affected when the mil light is on?? All those nice questions us tech's like to ask.:)
 

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nickb2

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#10
You state you suspect it was the downstream sensor which in my language means B1S2 sensor. Check for heater circuit in conjunction with codes P0037, P0038 and P0141.

P0136-139 are for oxygen sensor circuit malfunction, B1S2.

Provided are flow charts for those codes if they are to appear. Although I feel I am getting ahead of myself since you have not posted yet a code.

First PDF is for o2 sensor circuit malfunction, and second pdf is for heater circuit malfunction. Both for sensor 2.
 

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GM Guy

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Update-- The CEL came on again and the codes are P0136 and P0137. Do I understand correctly that the P0137 is outright failure of the O2 sensor? It looks like the heater failed. attached is the screenshot of the captured data when the CEL set.
 

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abrad

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#12
Just to toss in my $.02, check your mass airflow (maf) sensor. Sometimes just a shot of electric parts cleaner is all it needs (before tossing and replacing parts). The wife's car has that problem, keeps setting an o2 code when in reality it's the maf...
 

nickb2

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#13
looking at that 0% short term fuel trim on bank 1 sensor 1, that is ideal. Almost too perfect.

I see you were cruising under light load which tells me that O2 is working but the ECM did not code the heater circuit. Output voltage of B1S2 is at 0.585v which indicates it is a bit to high. Which would leave me to believe that engine is purring right.

Your throttle position mimes the calculated load. So no problem there also. After seeing that PID data, I safely can say to change that O2 sensor if all relating wiring is kosher.

Thanks for the picture, goes to show you are dedicated to fixing this.
 
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nickb2

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#14
Normal switching should be at about 0.45v and slow switching is normal as it is just correcting the pre cat sensor. You may see an increase in gas mileage, but a post cat sensor rarely causes driveability issues unless they are shorted to ground.

Although the following link is for a P0157, it is worth it to read to grasp a full understanding of your problem.

http://www.obd-codes.com/p0157
 

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#15
I'm Sorry this is so late.
This problem is FIXED with the replacement of the rear-most O2 sensor.