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Discussion Starter · #1 ·
Bank 1 Sensor 1 Fuel Trim (OBDII Data) -2.4 %
Bank 1 Sensor 1 Voltage (OBDII Data) 0.705 V
Bank 1 Sensor 2 Fuel Trim (OBDII Data) -2.4 %
Bank 1 Sensor 2 Voltage (OBDII Data) 0.445 V

What can one tell from information like this??
 

· ECU Tuner
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MmmotorNutz said:
Bank 1 Sensor 1 Fuel Trim (OBDII Data) -2.4 %
Bank 1 Sensor 1 Voltage (OBDII Data) 0.705 V
Bank 1 Sensor 2 Fuel Trim (OBDII Data) -2.4 %
Bank 1 Sensor 2 Voltage (OBDII Data) 0.445 V

What can one tell from information like this??
I'd say Sensors 1 and 2 are the primary and secondary oxygen sensors. They each generate voltages in the zero to one volt range. My guess is that those voltages then translate into recommended short term fuel trim in percent. However, I have not yet figured out all the rules the ECU uses to determine fuel trim.
 

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conradb212 said:
I'd say Sensors 1 and 2 are the primary and secondary oxygen sensors. They each generate voltages in the zero to one volt range. My guess is that those voltages then translate into recommended short term fuel trim in percent. However, I have not yet figured out all the rules the ECU uses to determine fuel trim.
The fuel trim of -2.4% is the amount of fuel removed from the fuel maps to attain the desired AF ratio which is in the range of 14.3-14.9.

The front O2 voltage means little as the front O2 is a wideband which determines its AF from current.
 

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Isn't the displayed voltage simply a conversion of the current reading to a simulated voltage?

On my OBDII software I can see the primary O2 sensor pretty much doing what I would expect when I'm driving. Although it displays in volts I know the ECU is reading current.
 

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Discussion Starter · #5 ·
Oh okay now that makes sense, fuel trim duh :D ! My next question is, what if the voltages were to rise or decline, what does that represent? For example what would a 0.9V reading mean?
 

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MmmotorNutz said:
Oh okay now that makes sense, fuel trim duh :D ! My next question is, what if the voltages were to rise or decline, what does that represent? For example what would a 0.9V reading mean?
Without an accurate table of A/F ratio's to 02 output it's hard to say. But if the voltage values are comparable to a narrow band sensor and based on my data logging they are then .9v would give an A/F ratio of around 11.0

A typical narrow band O2 sensor gives the following A/F ratio's

mv A/F
20 16.0
40 15.9
50 15.7
60 15.4
80 14.8
120 14.7
160 14.6
200 14.5
500 14.4
600 14.3
640 14.2
680 14.1
720 14.0
760 13.9
800 13.2
840 12.5
900 11.0
940 9.9
960 9.3
1000 8.5
 

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Discussion Starter · #7 ·
iwilson said:
Without an accurate table of A/F ratio's to 02 output it's hard to say. But if the voltage values are comparable to a narrow band sensor and based on my data logging they are then .9v would give an A/F ratio of around 11.0

A typical narrow band O2 sensor gives the following A/F ratio's

mv A/F
20 16.0
40 15.9
50 15.7
60 15.4
80 14.8
120 14.7
160 14.6
200 14.5
500 14.4
600 14.3
640 14.2
680 14.1
720 14.0
760 13.9
800 13.2
840 12.5
900 11.0
940 9.9
960 9.3
1000 8.5
I need to save this somewhere :thumbsup: . Cool to know that my AF is ideal :D .
 

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MmmotorNutz said:
I need to save this somewhere :thumbsup: . Cool to know that my AF is ideal :D .
Hmmmm... I checked some of my datalogs and at 0.9 volts on the second oxygen sensor my AF is anywhere between 12.33 and 14.25.
 

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Upon consulting my data logging that theory goes out the window :(

My data indicates a much narrower indicated voltage. Only on WOT or shutoff does the voltage deviate much from around .645 volts. It's certainly not sweeping between .08 and .6 volts. Here's a chart showing the MAP vs. O2 sensor voltage over around 20min of motorway cruising and city driving.
 

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Hmm, some more digging perhaps explains things a little better. I've pinched this from a Subaru board..

EMS, the graph showing the response curve above and the one attached to this post are from a paper describing the Denso wideband sensor used in the 1997 Toyota Camry, the first LEV sold in the US. I believe the WRX's AF sensor response will be found to be similar, but perhaps not identical.

I want to explain a little more how the WRX sensor works. Its response (mA) varies based on both the exhaust gas air fuel ratio AND the voltage applied to it by the ECU. In the attached graph, wherever a verticle line representing a voltage crosses a horizontal line representing an AF ratio, then the output current is accurate and proportional to the AF ratio. The WRX's ECU can supply 2.8 to 3.2 volts to the positive side of the AF sensor and 2.4 to 2.7 volts to the negative side. This nets out to a voltage of between .1 and .8, whose lines I've drawn on the graph. When the ECU wants to read lean mixtures, it increases the voltage to the sensor. When it wants to read rich mixtures, it decreases the voltage.

When cold, the WRX tries to run the car as lean as possible (ideal AF for minimizing NOx is around 23:1). Thus the voltage will be close to .8V and the sensor current will be above 7mA. Under acceleration, the ECU will drop the voltage to near .1V and the sensor current will be around -11mA.

The paper says that the sensor's diffusion layer is made temperature independent by selection of the proper radius for the micro pore. However, I suspect this temperture independence is only true up to a certain temperature. The WRX's sensor is located at a very hot spot. If the WRX's sensor were accurate at all temperatures, then the ECU would always maintain closed-loop control of the A/F ratio, even at WOT.
Would like to hear what Hondata makes of all of this.
 

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