GM 12616125 Sensor Assembly, Heated Oxygen (Position 2, Post, Converter)

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Oxygen sensors in the exhaust manifold can be hard to loosen when cold. To avoid damage, run the engine briefly before shutting it off, but avoid burns. When servicing, handle the sensor carefully, avoid damaging the attached pigtail and connector, and keep contaminants away. Don't use cleaning solvents and ensure the silicone boot is correctly positioned. To replace, note there are four sensors; one in each manifold and one after each catalytic converter. For upstream sensors, remove the engine cover, disconnect the connector, remove the sensor, apply anti-seize compound to threads if reusing, and install securely. For downstream sensors, raise the vehicle, disconnect the sensor, unscrew it, apply anti-seize if reusing, and install securely.

To replace the upstream oxygen sensors, you need to first remove the engine cover. Then, disconnect the upstream oxygen sensor electrical connector and remove the sensor. If you are reinstalling the old sensor, apply anti-seize compound to the threads.

There are four oxygen sensors in total. One is located in each exhaust manifold, and one is located just after each catalytic converter.