MichaelBrown

Seriously… Every other recent question on this forum has been answered but no one can seem to give me some kind of guidance here?

I just want to verify that with the oxygen sensor signal plug disconnected there should be a constant 3.3 V is this correct? I’m getting this information from the factory service manual.

i’m trying to diagnose why my oxygen sensor warning light stays illuminated and if the above information is correct, this is my problem. I’m not getting any voltage on that circuit at all.


Where is the factory service manual for my car which states 3.3 V

bicylindrico

No. I doubt any MB service manual is stating this. An old pre-wideband O2 will generate up to around 1 volt and this is when the fuel mixture is rich. The voltage drops to close to zero when lean and will move back and forth between the two when the system is functioning. You can watch the voltage on the circuit when the engine is running and the circuit is connected to the sensor and in closed loop. Just ground the negative side of your meter.

bicylindrico

That connection is for the Lambda tester which is an analog gauge showing the duty cycle at the EHA. Unless you have a lambda tester then then that connector wont do you any good.

I doubt anyone knows what you are talking about. How would anyone know how to help you unless you ask and give specific vehicle details?

I remember early models having a relay that would turn on the O2 sensor light at 120k miles as that was the service interval for them. We would just unplug the relay, there was no resetting them