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 or 10 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.