Oxygen Sensor

OPERATION

With the exception of the 1983–84 Pick-up and the 1984 49–state Montero, all Mitsubishi engines use an oxygen sensor to aid in the control of the air/fuel mixture. The ideal mixture within the engine is 14.7 parts of air to one part of fuel. If this ratio can be maintained under all conditions, emissions will be kept to an absolute minimum. The trick is to inform the Engine Control Module (ECM) of any change in conditions so that it can react and make necessary changes. The oxygen sensor is one of many sensors which detect changes during driving.

Located in either the exhaust manifold or the exhaust pipe ahead of the catalytic converter, the oxygen sensor reads the amount of oxygen in the exhaust flow and generates a proportional electrical voltage. This voltage is transmitted to ECM which interprets it and sends necessary messages to fuel and air control components. Remember that the oxygen sensor is reading the result of combustion and reacting to it. If there is a problem in the air/fuel mixture entering the engine, the combustion will be imperfect and the oxygen sensor will generate a signal which shows the error. The signal does not necessarily indicate that the sensor has failed, only that it has detected a different oxygen concentration.

Since the oxygen sensor is the furthest "downstream'' in the combustion process, it essential to check all other sensors and controls on the engine before assuming this sensor to be bad. Obviously, if the engine is running inefficiently, replacing the oxygen sensor won't cure the problem; the new sensor will continue to correctly read the imperfect exhaust content. About the only failure common to all oxygen sensors is loose or corroded connectors in the electrical wires. If a trouble code indicates an oxygen sensor malfunction, the first place to look is at the connector, making sure the pins are clean and fit tightly together. The low voltages flowing in this system can be changed or blocked by a high resistance (poor) connection.