Oxygen Sensor Simulator

The oxygen sensor simulator as built on a protoboard. Note the cigarette lighter plug used for power source. The adjustment knob is at the left, and the switch is on the right. The red indicator LED is in the middle. Only use red, because the voltage drop of the LED is part of the circuit!

The schematic diagram for the simulator. Closing the switch engages the simulator. Turning the knob clockwise simulates a lean condition, turns the LED off, and the car should start running rich to compensate. The big "V" is a digital voltmeter(not shown in the pictures). Using a smaller value for C1, perhaps 4.7 uF, will make the circuit oscillate faster and might be more like a real oxygen sensor(a new sensor switches more often than an old one).

The adapter cable. Note the connector recycled from an old oxygen sensor. Hard to see under the black tape: 100K resistor.

The schematic diagram of the adapter cable and oxygen sensor. Note the heater is shown as a resistor, mine measured about 7 ohms.

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Frequently Asked Questions:

Q:

Will you build one of these for me, or sell me the one you built?

A:

No, I won’t do that. If there is a community college or high school near you with an electronics class, you should contact the instructor and ask if there are students looking for a small job. This project is simple enough it should not pose a problem.

 

 

Q:

I built the project but I have to fiddle with the knob all the time.

A:

The car eventually will get too rich or too lean because it isn’t using the oxygen sensor anymore. This is a diagnostic aid, not a long-term replacement for an oxygen sensor.

 

 

Q:

I do racing on the weekends with my street car. Will this project help me tune the car to different conditions?

A:

If you do drag racing, yes. The races are short enough you can set a mixture and it will hold long enough. Each time you start the car it will go to the mixture you set. Other forms of racing take too long, and the mixture will creep towards very rich, you’d have to adjust the knob while driving.

 

 

Q:

Is this thing legal to use in California on the road or at the track?

A:

I am not a lawyer, but I would guess it is legal as a diagnostic aid, for emergency use, and for off-road use. If it’s really important to you, consider it not legal or get a lawyer’s opinion. It is not a computer under NHRA general regulations section 9:1 so it should be legal for drag racing at any track in the US.

 

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