About 4 wires heated O2 sensor?

[wan520i]

Just changed new O2 sensor on my car, and just want to make sure that this expensive sensor is working... My question is about the heater wiring to the sensor.. Does anyone know when is 12 volt VDC supply to the sensor (for heating up)? and when it stop supply to it for stop heating up the sensor? Or will this sensor be heating as long as the engine is running? Thanks for your inputs...

 

[wan520i]

BUMP please..:help:

 

[goggomobil]

Sensor heating is to speed up getting the sensor to operating temperature on startup. Not sure what the control strategy whether heating remains on or cuts off after reaching temp. (but I think the heater is cut off).

If your sensor is not working you will know for sure, engine won't idle or run properly.

If you are really curious you can wire up a digital voltmeter to the 12v supply to the sensor and see it it cuts out after a few minutes, and you can also look at the output signal, if the sensor is performing you will see the voltage swing between 0.2 and 0.8 V with frequency about 1 second.

Just changed new O2 sensor on my car, and just want to make sure that this expensive sensor is working...

My question is about the heater wiring to the sensor..

Does anyone know when is 12 volt VDC supply to the sensor (for heating up)? and when it stop supply to it for stop heating up the sensor? Or will this sensor be heating as long as the engine is running?

Thanks for your inputs...

 

[turbology]

When you find your mileage (km per tank of gas) goes up, you know your O2 sensor(s) is doing its job.

Is hard to tell O2 sensor is working without a diagnostic tools.

 

[astroboy]

I read some where by just measuring the ohm (resistance), one will know if the O2 sensor is working at its optimum sensitivity.

 

[turbology]

I read some where by just measuring the ohm (resistance), one will know if the O2 sensor is working at its optimum sensitivity.

The 'some where' you read is not accurate

 

[wan520i]

If you are really curious you can wire up a digital voltmeter to the 12v supply to the sensor and see it it cuts out after a few minutes, and you can also look at the output signal, if the sensor is performing you will see the voltage swing between 0.2 and 0.8 V with frequency about 1 second.

I had check with a digital meter to the 12v supply at the sensor connector - 2 white wires, when the engine is cold, warm or hot, there is no 12v VDC present for heater.

Also checked the O2 sensor relay, it seems ok to me.
There are 4 wires at the relay:
Terminal 30 & 86= red/white-12 volts VDC.
Terminal 87= green-to O2 sensor.
Terminal 85= brown/green-output from DME.

I believe terminal 85 is ground wire, but measured with a digital meter found 12volt VDC present there. Just don't know WHEN is the smart DME will convert it become "Ground"?

So far my car idling is fine, but I think my fuel consumption is quite high especially on city drive, is about 0.37 cents per km based on old petrol price, highway is about 0.23 cents per km.

 

[pussy]

sorry wan.. very hard question, never went into this field...

regards.

 

[turbology]

From the E36 Bentley manual (i know yours is E34, but it might be similar ):
1. Connect the DIGITAL voltmeter to connect 1 and connector 2 on O2 sensor, start the engine, the output of voltage will fluctuating a short period of time. (0.2-0.8VDC)

2. If incorrect: Seperate sensor harness connect from sensor. Check for battery voltage between terminals 3 & 4 (green wire & brown wire) while engine is running. If voltage is not present, check your oxygen sensor heater relay.

3. Check heater element resistance between terminal 3 & 4 of SENSOR. If the sensor's element has no continuity, replace sensor. If the preheater circuit is ok but the sensor doesn't product a fluctuating voltage, replace sensor.

In the manual: To check sensor respone to lean and rich condition, create an air leak, or pull vacuum hose off the fuel pressure regulator to increase fuel pressure.
You shall see the output voltage fluctuate.

Tightening torque : Oxygen sensor to exhaust pipe - 41 ft-lb

 

[turbology]

The working temperature of O2 sensor must exceed 575F (300C) for it output correct voltage (for lean and rich condition)

Remove the sensor. Start the car. Use an infraRed temperature sensor to check the surface temperature.

 

[wan520i]

Thanks to turbology for your lengthy write up from bentley manual, I have the manual for e34, too.

Also big thanks to others for your replies..

To my understanding, the heater should be "ON" when the engine is cold, and "OFF" when the engine is hot or reach certain temperature..., some sensors have to tell DME about it, probably engine coolant temperature sensor..& ???

Still searching answer for the above..., pls help.

 

[turbology]

Conductivity change when temperature change.
Conductivity drop when temperature increase.

My theory to your question: when sensor's temperature get really hot, it resistance to eletrical flow increase. When the reistance increase, less current is flowing through the sensor, thus keeping the O2 sensor at right temperature.

Hope this help

 

[wan520i]

turbology, refer to your theory, is that means 12volts VDC is supply to the O2 heater, as long as the engine is running?

 

[turbology]

Yes. At least i think so

And it make sense with 2 and 3 at earlier post