Mercury 5C5Z-9F472-AA Sensor - Hego

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When servicing an oxygen sensor, special care is essential due to the permanently attached pigtail and electrical connector that cannot be removed; any damage or removal will ruin the sensor. It is important to keep grease, dirt, and other contaminants away from the electrical connector and the louvered end of the sensor, and cleaning solvents should never be used on an oxygen sensor or air/fuel ratio sensor. Avoid dropping or roughly handling the sensor, and ensure the silicone boot is installed correctly to prevent melting and ensure proper operation. Since oxygen sensors are located in the exhaust system, which contracts when cool, they may be difficult to loosen when the engine is cold; starting the engine for a minute or two can help. Begin by disconnecting the cable from the negative terminal of the battery and securely raising the vehicle on jackstands. There are two upstream oxygen sensors on all models, with specific locations depending on the engine type. Locate the desired upstream oxygen sensor, trace the lead to the electrical connector, and disconnect it before using a special oxygen sensor socket to unscrew the sensor. Clean the threads of the sensor bore in the exhaust manifold after removing the old sensor. If reinstalling the old sensor, apply anti-seize compound to the threads; for a new sensor, this is unnecessary as they come pre-coated. Installation follows the reverse order of removal, ensuring the sensor is tightened to the specified torque. For downstream oxygen sensors, which are also present in pairs, disconnect the electrical connector before unscrewing and removing the sensor. Clean the threads of the sensor bore in the catalytic converter, apply anti-seize compound if reinstalling the old sensor, and remember that new sensors do not require this. Again, installation is the reverse of removal, with attention to proper torque during tightening.

1. Disconnect the negative battery terminal. 2. Remove the exhaust manifold heat shield. 3. Disconnect the upstream oxygen sensor electrical connector. 4. Unscrew the upstream oxygen sensor using an oxygen sensor socket. 5. Apply anti-seize compound if reinstalling the old sensor. 6. Install the sensor and tighten it to the specified torque. 7. Reconnect the battery and allow the PCM to relearn its idle and fuel trim strategy.

An oxygen sensor is a galvanic battery that produces a very small voltage output in response to the amount of oxygen in the exhaust gases. This voltage signal is the "input" side of the feedback loop between the oxygen sensor and the Powertrain Control Module (PCM).