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Discussion Starter #1
Hi there,

I have a problem with the downstream oxygen sensor and the ecu

I got check engine light with p0138 error code.
I scanned the scar and noticed that the voltage on the downstream oxygen sensor is constant 1.3 volts. The sensor was removed from the car and tested with a torch and a multi-meter Technically seems to work ok.
However there is something weird. I scanned the car without the sensor connected and the voltage stays the same - 1.3 volts on the ecu.

I also scanned the voltage on the o2 plug coming to the ecu.
I got 12v on the heater wires and 4.35 volts coming down to the oxygen sensor (from ecu) (positive and ground wires).

Can you please help me to diagnose what's going on ?
 

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...I got 12v on the heater wires and 4.35 volts coming down to the oxygen sensor (from ecu) ....
Both voltages OK. 4.35 open Volts from ECU is normal.
Welcome to the forum. In order to know you more, please fill up your profile, where are you, car type, year, AWD?..transmisison..etc. ...
 

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Discussion Starter #4
Oh you got me :) 2008 SX4 AWD automatic. Regarding the voltage - why my android scanner shows 1.3V for that o2 sensor? Shouldn't be 0V when disconnected?

Technically the scanner shows 1.3v either connected or disconnected and pops up with p0138 code...
 

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Discussion Starter #6
I know what that code means. The problem is that I see that code even though the sensor is disconnected...
 

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Discussion Starter #7
unless there is an open circuit and 1.3v means that the sensor is broken.
Is there anyone how could check that on their car? like unplugging the downstream sensor and checking what voltage appears one the scanner .. I know it's a lot to ask for.
 

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Why dont you verify the circuit?

Unplug at ECU and check for voltage drop/ground/shorts.. If the circuit proves viable.. all is left is the sensor..

As an after though, what are the Fuel trims and the B1S1...

... Philip
 

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Discussion Starter #9
How can I check the wires for shorts. You mean the hot (positive) one with both heater wires and the ground (negative) with the hot (positive) right?
I suspect that the wires are ok - already getting 12v on the heater wires and ~5v on the hot and ground (negative) wires. if there was a broken wire I couldn't get the right voltage on the plug coming from the ecu

The A/F sensor is brand new.
 

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I suggested in post 8, do you not understand how to verify the circuits, or do you wish to keep guessing?

If you unplug from ECU (power OFF)they should all be open, no shorts to ground, when tested from sensor plug.

Baring that, employ an auto electrician...

... Philip
 

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Discussion Starter #13
So, I checked the wires against shorts or breaks. unplugged the ecu plugs, checked if there are any issues with the wires and all looks good.
There must be either the o2 sensor shot or something wrong with the ecu. Would be a good idea to call a Suzuki dealer and ask for the voltage but there is no Suzuki in Canada anymore...
 

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Discussion Starter #14
Hi,
So I ended up with a o2 simulator with apparently doesn't work with sx4. The good thing is that that 1.3 v was the bias voltage being read by the ecu.
The downstream O2 was broken - that was the reason why I was getting that bias voltage
Right now the voltage fluctuates from 0 - 0.95v which is good (at least in the theory)
But the ecu gives me grief with p2096 error code.
I'm assuming that 02 simulator is not just compatible with my sx4.
BTW I bought is from MAGNUM Tuning Performance & Fuel Saver Parts - Accessories * Auto & Powersport upgrades - Manufacturer
 

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Did you perform a voltage drop test on the wires, a MM does not always tell the truth when you have a high resistance circuit.. The simulator would probably work if the circuit was clear..

I presume the switching 0-.95vdc was on the B1S1... If on the S2, that is not correct..

http://www.obd-codes.com/p2096.

... Philip
 

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Discussion Starter #16
The voltage is correct - that was confirmed by Magnum Tuning. The voltage goes from 0V up to 1.0V.
0.95V was recommended by them for my car. I changed the voltage to the recommended value but the error (p2096) still persists.
The sim was designer to emulate the downstream oxygen sensor. I followed the manual and double tested the setup. 0 - 0.95V comes from the sim which is hooked up to the downstream harness/plug so it's the B1S2. My assumption (maybe false) is that they used 555 timer which only goes from 0v to 1.0v and they didn't use any capacitors. I maybe wrong but on my scanner the voltage goes from 0v to 0.95v and back to 0v pretty fast and that doesn't look like the values I was getting from the real o2 sensor before. Maybe the ecu is just too smart ....
 

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You have the wrong information,,

The B1S2 is post CAT and should be an almost steady 0.45-0.55vdc when the cat is working, any out of that range will set a code... this sensor monitors the CAT condition only

The B1S1 is the one that switches as it helps control the fuel/air ratio..

... Philip
 

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Discussion Starter #18
Regarding the voltage you mentioned. That's what I though - I recall that the optimal voltage should be approx 0.5vdc. I mentioned that in an email I sent to Magnum and those guys told me I'm wrong and voltage should be 0.9 -0.95 vdc. I think that they just don't want me to return the sim...
When I lowered the voltage to 0.6vcd, I was getting a different code - p2a01
 

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Discussion Starter #20
I use elm327 and Piston app.
Back to the square one again..
Probably the best solution would be to buy a new cat and o2 sensor..

Thanks for your help
 
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