What is the signal that a oxygen sensor produce to ECM when working properly ?

 

A wildly flickering voltage between 0 and 1 volt.

 

I'd like to create an oxygen sensor emulator , 0-1 volts isn't helping me much !

Is there a sequence ? What's the difference between a signal from a bad and a good O2 sensor ? anybody knowns ?

 

The O2 sensor, when heated to operating temperature, will produce a voltage greater than approx 450 mv when rich of the stoiciometric afr (14.7:1), and will produce a voltage of approx less than 450 mv when lean of stoich. The O2 sensor is a very high impedance voltage source, so it may not be loaded with a low impedance (analog) voltmeter - a digital meter must be used to measure its output voltage. As the sensors age, their response time to afr change decreases.

 

Maybe I'm misunderstanding, but are you asking how you could produce the low output voltage normally supplied by the ECM so you can read your A/F ratio with a multimeter, totally separate of the ecm? If so, I don't really have the answer, but I wonder if you could use the multimeter to read the resistance across the sensor instead of the voltage drop? I'm not sure, but doesn't the multimeter put out a low voltage to read resistance? I'm a little rusty with the math, but there definitly is a way to derive the resistance change from the set voltage change of the sensor.

 

The O2 sensor actually produces a voltage, unlike the other passive (resistive) sensors, which require a voltage source. The ECM supplies a high impedance bias of approx 450 mv to the O2 sensor, as the O2 sensor is an "open circuit" when it is cold. When it heats up to operating temperature, it is able to overcome the bias from the ECM, and its voltage output varies with change in afr. The O2 sensor output voltage may be read directly from the sensor. A potentiometer may be used as a manual variable voltage source to the ECM O2 sensor input to simulate the O2 voltage to the ECM. The voltage range is 0 (lean) to 1 (rich) volt.

 

The O2 is essentially a battery of sorts. Never use an ohmmeter to test one. The voltage the meter puts out to measure across a resistor will destroy the sensitive junction in the sensor. The 450mv Tim refers to is to keep a slight pullup voltage on the input line for the sensor during the time the sensor has zero output. They need to get to approx 500-600 degrees to produce a signal. Also make sure if you measure the sensor output your meter has an input impedance of at least 10M-ohms otherwise you will draw excessive current and either get an erroneous reading or destroy it.

 

Very cool, thanks for the answers. Will put my creation into motion.