Oxygen sensor


wire installation on vehicle:

red wire:12v source e.g 12v ignition or 12v ACC.not 12v battery! (it shouldn't stay on when the key is removed.)

Black wire:ground source. any ground source will do as all ground connections should be the same.

green wire: signal wire. this must go to the oxygen sensor's signal out, in parallel with the ECU. not in series!
(this is usually a blue or black wire). If your not sure which wire is the signal wire, then just put a multimeter on at a time until you measure a wire that has a voltage range of OV-1V

NOTE: this unit will only work with a narrow band oxygen sensor (OV-1V)

background:

This display unit is designed to show an oxygen sensor's voltage reading which it obtains from the air/fuel mixture after combustion . It does this by lighting up LEDs to show the different conditions of air/fuel mixture.

It uses an "IC' chip called the LM324 comparator. This chip compares the voltage from the oxygen sensor to a preset voltage from the resistors on the pcb.

Basically the series resistors have two voltages which it uses to compare it with the O2 sensor Voltage.

This being 0.23V and 0.63V.

This following is a comparison is to show what will happen at different conditions of the sensor voltage.


Oxygen sensor's                         Led colour:                      Air/fuel ratio
voltage:

Less the 0.23V                            green                             Lean
between 0.23V & 0.63V             yellow                           stoich (14.7:1)
Above 0.63 V                             red                                Rich


A basic guide on the LED sequence:

Initial start-up= green led. This is simulating a lean condition as the O2 sensor can't produce a voltage yet because it hasn't warmed up enough.However there are ECU's that send out a voltage to the O2 sensor
at initial start-up to simulate the actual rich condition when cold.

After 10sec-3mins=red LED.Depending if it's a heated O2 sensor or non-heated it should gradually start to go from green to yellow and then to red and stay on red.This is because the engine runs rich when it's cold.

After 4mins-7mins= all LEDs.again depending on if it's a heated or non heated O2 sensor, the system should  gradually go into closed loop as the engine warms up.And then the engine will cycle from lean to rich lighting up each LED in sequence.

Full acceleration=red LED. With the throttle fully open,the red LED will as it's indicating a rich mixture.

Deceleration= greed LED.after letting go the throttle from full throttle , the system should go learnas the injectors should be squirting in a very low amount of fuel or none at all.