Nissan Pick-ups and Pathfinder 1970-1988

Oxygen Sensor



Gasoline Engines Only

The three-way catalytic converter, which is capable of reducing HC, CO and NOx into CO 2 , H 2 O, O 2 and N 2 can only function as long as the air/fuel mixture is kept within a critically precise range. The oxygen sensor system is what keeps the oxygen range in control.

Basically, the oxygen sensor system works like this: As soon as the engine warms up, the computer begins to work. The oxygen sensor, located in the exhaust manifold, senses the oxygen content of the exhaust gases which varies according to the air/fuel mixture. The O 2 sensor produces a small voltage that varies depending on the amount of oxygen in the exhaust at the time. This voltage is picked up by the ECU. The computer works together with the fuel distributor and together they will vary the amount of fuel which is delivered to the engine at any given time.

If the amount of oxygen in the exhaust system is low, which indicates a rich mixture, the sensor voltage will be high. The higher the voltage signal sent to the computer, the more it will reduce the amount of fuel supplied to the engine. The amount of fuel is reduced until the amount of oxygen in the exhaust system increases, indicating a lean mixture. When the mixture is lean, the sensor will send a low voltage signal to the computer. The computer will then increase the quantity of fuel until the sensor voltage increases again. Then the cycle will start all over.


The oxygen sensor is installed in the exhaust manifold and is removed in the same manner as a spark plug. Exercise care when handling the sensor do not drop or handle the sensor roughly. Care should be used not to get compound on the sensor itself.

  1. Disconnect the negative battery cable.
  3. Unplug the wiring connector leading from the O 2 sensor.

Be careful not to bend the waterproof hose as the oxygen sensor will not function properly if the air passage is blocked.

  1. Unscrew the sensor from the exhaust manifold.

To install:
  1. Coat the threads of the replacement sensor with a nickel base anti-seize compound. Do not use other types of compounds, since they may electrically insulate the sensor. Do not get compound on sensor housing. Install the sensor into the manifold. Installation torque for the sensor is about 18-25 ft. lbs. (24-34 Nm). Connect the electrical lead. Be careful handling the electrical lead. It is easily damaged.
  3. Reconnect the battery cable.