Update, HELP NEEDED, O2 Sensor 3.8 volts???

[lmdew]

Thanks for the update Imdew. Glad you got it fixed. Does the voltage across the sensor drop to a normal level (0v to 1V) when the car starts to warm up?

 

Nope, it stays up around 3.8 volts, with the normal up and down spikes for an O2 sensor, so 2.8 - 4.5 which is way high. I guess that's the way this car is set, as the ECU is happy.

[Cougar]

Interesting. I have to assume that it is the way it was designed to work. Thanks.

[Wayne Boncyk]

Hey, Larry - it seems odd to me that there'd be a bias voltage on your particular O2 sensor arrangement. I don't think I've heard of another sensor that worked that way. This leads me to ask the question, have you checked the calibration of your voltmeter lately? If not, then try to read the voltage of a D-cell battery. If you come up with anything grossly different than 1.5V, you may have to adjust your meter.

[Wayne Boncyk]

Hey, Larry - it seems odd to me that there'd be a bias voltage on your particular O2 sensor arrangement. I don't think I've heard of another sensor that worked that way. This leads me to ask the question, have you checked the calibration of your voltmeter lately? If not, then try to read the voltage of a D-cell battery. If you come up with anything grossly different than 1.5V, you may have to adjust your meter.

 

I withdraw this comment! I should have read all the posts in-between when I first commented and these latest ones. I guess your ECU is happy to bias up the O2 sensor by nearly 4 volts! Again, I haven't seen any other system doing that, so there is probably a bias resistor (or a coupling capacitor) shorted in your ECU. That MIGHT lead to premature failure of the O2 sensor, but I've never had one biased up like that before so I can't say that for sure.

 

If your replacement sensor fails before too long and it "sticks" at 3.8V again, then you'll know you need to change the ECU at that time!

[lmdew]

The ECU was the first thing I tried, a used one. The readings were the same. Not positive, but with two doing the same thing, I'm happy to make the leap and say that is what the system is looking for. If someone had a same make and model that would be a nice check. I read it out with my OBDII reader and the Fluke 87. There you go.

[ShawnW]

Maybe its the meter? Ive remember for some things you are better off with a cheapie analog type than higher end fluke....

[Cougar]

Shawn,

 

I think this circuit has a high input impedence so you would want to use a meter that has a high input impedence, like a digital meter, to measure voltage with.