Audi A4 Install Oxygen Sensor
The emissions control system in the Audi A4 uses an oxygen (O2) sensor to measure the amount of oxygen in the engine exhaust. The sensor transmits this data to the vehicle's computer by means of an electrical wire. The computer interprets the data and makes adjustments to the air/fuel mixture while the engine is running. This helps the engine operate at peak efficiency, thereby reducing exhaust pollutants. The O2 sensor requires periodic replacement, and many owners can change it themselves.
Oxygen sensor socket and ratchet
Install Oxygen Sensor
- Park the vehicle, set the parking brake, shut off the engine and open the hood. Wait for the engine and exhaust system to cool completely, before proceeding, to avoid burns.
- Locate the sensors; there are two of them. The upstream is threaded into the exhaust manifold, which is in the lower engine area on the passenger's side, below the exhaust pipe flange and before the catalytic converter. The downstream sensor is threaded into the exhaust pipe after the catalytic converter.
- Spray penetrating lubricant at the base of each sensor and let it set in for 30 minutes before proceeding. This will help loosen the sensor for easier removal.
- Unplug the sensor wire on the upper (upstream) sensor from the vehicle's connector. Back out the sensor by rotating it counterclockwise with a sensor socket and ratchet. Insert the new sensor into the hole and tighten it with the sensor socket, using a clockwise rotation. Connect the sensor wire to the connector on the vehicle.
- Repeat Step 4 for the lower (downstream) sensor.