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certified idiot
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694 Posts
for some reason your post is just showing quotes so I have no idea of what you are trying to say?
Can you retype it?
all I see is
"Bank 2 sensor 1 is reading ".4v".. I'll start the car and about 30 seconds drop out to ".0".. If i unplug"
 

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2001 Disco 2 SE no ACE 115k miles
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71 Posts
Discussion Starter · #3 ·
I have 3 days left to pass inspection.. With the car sitting and the key turned to the accessory position.. Bank 2 sensor 1 is reading .4volts..
I'll start the car and about 30 seconds it will drop out to .0volts.. If i unplug the sensor it will read .4v again.. The exhaust smell is not of rotten eggs but more of a gas like.. What is the proper Bosch Replacement? Is it the 15175?? Course of action please??
 

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certified idiot
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694 Posts
thats really wierd!
yes the O2 sensor is the bosch 15175

however when you unplug it you should get a 0v reading as the sensor generates the voltage - no connection no voltage! are you reading live data and not looking at assumed parameters for default driving?
I dont know any condition other than a damaged harness or shorted connector (heater wire running into the sensor wire) that would give you a voltage reading from the sensor when its unplugged and you are reading live data. The heat of the gasses burning across the zirconium bulb in the sensor generates the voltage, nothing is supplied other than to the heater element.
remember too when installing the sensor never put sealant or di-electirc grease in the connector socket as the sensor need to breathe through the wires and if you totally seal the connector the sensor doesnt get enough air movement (as tiny as it is) and can stop working.
cheers
Barri
 

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certified idiot
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694 Posts
An oxygen sensor doesnt get supplied with any voltage from the car, the basic sensor itself can be one or 2 wires, if its one then the wire caries voltage generated by the sensor bulb into the ecu, 2 wire have a ground wire so the sensor creates a loop of voltage and ground to the ecu.
In order for the o2 sensor to work efficiently when cold at startup they started to heat them with power from the car so added 2 heater wires a power and a ground. The only power supplied to the sensor then is the power to the heater.

the sensor puts out more voltage the hotter it gets so the richer the mix the higher the voltage from the sensor

we have a 4 wire system and typically the bosch has 2 white wires going into the sensor one a heater ground and one a heater power wire. the other 2 wires are sensor signal (usually bosch black) and sensor ground (bosch usually uses grey).

If you physically unplug the O2 sensor then there can be no signal to the ecu as the sensor makes the voltage for its signal - it should read 0v unplugged on a live data feed - if it doesn't read 0v then you have to be getting voltage from somewhere else and the only place that can come from in the o2 wiring harness is some sort of short from the heater power supply.

If you are not reading actual live data then all bets are off.

If you replaced your original sensor with a knockoff - a lot of them have the wires in the wrong order in the plug, its fairly easy to find the wires you need though with a voltmeter.

If you put silicon sealant in the plug to waterproof it then throw the sensor away and buy another one and dont put anything in the plug not even di-electric grease.

Most sensors even with the heater and those with SAI will run close to 0v for the first 30 seconds or so , once they start to get hot (over 30 seconds) the front sensor on a SAI engine will sit around .2 -.4v and a non SAI engine will go up to .7-.8v. Generally the first 2 minutes of operation are all over the place as the ecu runs choke cycle for about 900 revolutions of the engine - 300 revolutions at full choke cycle - double firing from the injectors - then decreasing over the next 600 or so revolutions of the engine to normal pulse. You only really get stoichiometric running in closed loop once the engine is up to temp - thats why the testing stations always used to ask you to get there with a hot engine.

hope that is some help
Barri
 

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Now that's a complete answer!
Nice one Barri
Should help lots of people understand what it does and how it does it
Thanks
 
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