GM 12561777 Sensor Assembly, Heated Oxygen

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The oxygen sensor is situated in the exhaust manifold for 4 cylinder models and in the left exhaust manifold for the V6 cars and it measures the oxygen content of the exhaust gas and provides a standard voltage output, which ranges between 0.1 volts in relationship to high oxygen or lean fuel mixture and 0.9 volts for low oxygen or rich mixture. The PCM utilizes this fluctuating voltage to manage the air/fuel mixture proportion in an effort to achieve an ideal of 14.7 ratio of air to one of fuel to reduce emission and optimize the function of catalytic converters. Engines with TBI, four-cylinder and V6, have an oxygen sensor while the V6 engines with CMFI and CSFI have three sensors. The sensor does not generate voltage below its normal working temperature of about 600-degrees F (360-degrees C), so during start up the PCM takes no input and hence runs in an open loop. If the engine gets to normal temperature, and the sensor gives a constant voltage of 0.35 - 0.55V, then a trouble code might be logged if, for instance TPS indicates that the engine is not idling . It is also possible for a sensor to take longer time in performing a function or for the voltage signals to be out of the usual range and this, in turn, causes trouble codes to be set because the PCM will then have to control the fuel delivery with the default settings it has rather than relying on the signals from the sensors. In order to function correctly a sensor requires good electrical connections, free flow of air, correct temperature and the ability to work with unleaded fuel. When servicing caution must be taken in such areas as; damaging the pigtails and connectors which are permanently attached, preventing contaminants from coming into contact with the electrical connector and sensor end, and positioning the silicone boot correctly. On some models there will be come a time to replace the said sensor, and at this time it may prove difficult to loosen if the engine is cold, in this case what needs to be done is to run the engine for several minutes. Transmission data Link sensor wiring should be disconnected from harness, the battery's negative terminal should be disconnected and vehicle raised and safely supported. The sensor should be delicately undone from the exhaust manifold and before doing this, a application of the anti - seize compound on the threads will be appropriate once the sensor is re-installed you will reconnect the electrical connector and then raise/lower the vehicle to reconnect the battery.

Clear the PCM of all trouble codes by removing the PCM-B fuse or disconnecting the cable from the negative terminal of the battery for at least 30 seconds.