GM 91177408 Sensor, Oxygen (On Illus)

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The oxygen sensor is a crucial component in the exhaust system that monitors the oxygen content of the exhaust gas stream. It produces a voltage signal that corresponds to the amount of oxygen present in the exhaust gases. This signal is sent to the PCM, which uses it to determine the correct amount of fuel to inject into the intake passages in order to maintain the ideal air/fuel ratio of 14.7:1. The oxygen sensor operates in "open-loop" mode when it is below its normal operating temperature, but once it has warmed up, it produces a signal voltage that fluctuates between 1.0-volt and 0.1 volt. There are two heated oxygen sensors on OBD-II vehicles: the upstream sensor, located in the exhaust manifold, and the downstream sensor, located after the catalytic converter. The downstream sensor allows the PCM to monitor the effectiveness of the catalytic converter. A problem in the oxygen sensor circuit can result in various diagnostic trouble codes, and it is important to check other components and systems that may affect the air/fuel mixture or combustion quality before determining if the sensor is defective. Testing the oxygen sensor involves measuring the voltage output under different engine conditions. If the sensor does not function as described, it should be replaced. When replacing the sensor, it is important to disconnect the negative battery cable, unplug the sensor connector, and use a special oxygen sensor wrench to carefully remove and install the sensor. The threads of the new sensor should be coated with anti-seize compound and tightened to the specified torque.

Before installing it in the manifold, coat the threads with an anti-seize compound.