Oxygen sensor / air-fuel ratio sensor — replacement
Note: The manufacturer refers to the upstream (before the catalytic converter) sensor as the air-fuel ratio sensor, and the downstream sensor (after the catalytic converter) as the oxygen sensor.
Note: Because it is installed in the exhaust manifold or pipe, which contract when cool, the oxygen sensor may be very difficult to loosen when the engine is cold. Rather than risk damage to the sensor (assuming you are planning to reuse it in another manifold or pipe), start and run the engine for a minute or two, then shut it off. Be careful not to burn yourself during the following procedure.
1. Disconnect the cable from the negative battery terminal (see Engine electrical systems).
2. If you’re replacing the downstream sensor (s), raise the vehicle and support it securely on jack stands. Remove the lower engine cover. Access the oxygen sensor harness (see illustration) and unplug the electrical connector.
12.2a Downstream oxygen sensor details four-cylinder models
A Sensor electrical connector
B Sensor
12.2b Downstream oxygen sensor details — V6 models
A Bank 1, sensor 2
B Bank 2, sensor 2
Note: On V6 models, Bank 1 is on the #1-cylinder side and Bank 2 is on the opposite side (see illustration).
3. The upstream sensor (also called the air-fuel ratio sensor) can be replaced without raising the vehicle (see illustration). Unplug the sensor electrical connector.
12.3 Location of the upstream oxygen sensor (or air/fuel ratio sensor) — four-cylinder models
4. Unscrew the sensor from the exhaust manifold (s) or exhaust pipe (see illustration). Note: The best tool for removing an oxygen sensor is a special slotted socket, especially if you’re planning to reuse a sensor. If you don’t have this tool, and you plan to reuse the sensor, be extremely careful when unscrewing the sensor.
12.4 Use a slotted socket to remove the oxygen sensors
5. Apply anti-seize compound to the threads of the sensor to facilitate future removal. The threads of new sensors should already be coated with this compound, but if you’re planning to reuse an old sensor, recoat the threads. Install the sensor and tighten it securely.
6. Reconnect the electrical connector of the pigtail lead to the main wiring harness.