Oxygen sensors — general information and replacement Ford F150
General information
1. All models covered by this manual have On-Board Diagnostics II (OBD-II) engine management systems, which means that they have the ability to verify the accuracy of the basic feedback loop between the oxygen sensor and the PCM. They accomplish this by using an oxygen sensor in front of the catalytic converter and an oxygen sensor behind the catalytic converter. By sampling the exhaust gas before and after the catalytic converter, the PCM can determine the efficiency of the converter and can even predict when it will fail.
2. The primary (upstream) oxygen sensor is located in the exhaust pipe or manifold and the secondary (downstream) oxygen sensor is located on or behind the catalytic converter. The upstream and downstream oxygen sensors on all models is a heated oxygen sensor. The PCM uses a supply wire and ground wire to control the power to the 02 sensor heater during warm-up.
Note: The downstream oxygen sensors may also be referred to as Catalyst Monitor Sensor (CMS).
3. Special care must be taken whenever a sensor is serviced.
- Oxygen sensors have a permanently attached pigtail and an electrical connector which should not be removed frOm the sensor. Damage or removal of the pigtail or electrical connector can adversely affect operation of the sensor.
- Grease, dirt and other contaminants should be kept away from the electrical connector and the louvered end of the
- Do not use cleaning solvents of any kind on an oxygen sensor.
- Do not drop or roughly handle an oxygen
- The silicone boot must be installed in the correct position to prevent the boot from being melted and to allow the sensor to operate properly.
Replacement
Note: Because it is installed in the exhaust manifold or pipe, which contracts 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.
Oxygen sensor electrical connectors (top of transmission) — right cylinder bank (2.7L model shown)
Oxygen sensor electrical connectors (attached to a bracket near the rear of the transmission) — left cylinder bank (2.7L model shown)
4. Raise the vehicle and support it securely on jackstands. Access the oxygen sensor harness and unplug the electrical connector.
Upstream (A) and downstream (B) oxygen sensors — left cylinder bank shown, right bank similar (2.7L model shown)
If available, use a slotted socket to remove the oxygen sensor
5. Unscrew the sensor from the exhaust manifold or exhaust pipe 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.
Applying anti-seize compound to an oxygen sensor (new sensors should already be coated)
6. if the old sensor is to be installed, 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.
7. Reconnect the electrical connector of the pigtail lead to the main wiring harness.
8. Lower the vehicle, test drive the car and verify that no trouble codes have been set.