By determining the composition of the exhaust gases before and after the catalytic converter, the PCM determines the efficiency of the catalytic converter.
Figure 7.16. Location of oxygen sensors on models since 2001: 1 – electrical connectors; 2 – oxygen sensor (block 2, sensor 2); 3 – oxygen sensor (block 1, sensor 2)
Primary (in the direction of movement of exhaust gases) the oxygen sensor is located in the exhaust manifold or in the tailpipe, and the secondary one is located behind the catalytic converter (figure 7.16).
Caution! Do not confuse the oxygen and air-fuel mixture sensors. They are similar in appearance, but they work differently and have different performance characteristics.
Like the oxygen sensor, the air fuel ratio sensor converts information into an output voltage that is transmitted to the engine control unit. The signal magnitude is proportional to the air/fuel mixture ratio in the exhaust gas flow. The air-fuel ratio sensor changes the output voltage from 3.3 to 3.0 V depending on the proportion of oxygen in the exhaust gas stream. Like the oxygen sensor, the air-fuel ratio sensor only begins to function properly after warming up, for which purpose heaters are installed on the sensors.
When servicing sensors take the following precautions:
The oxygen and air-fuel ratio sensors have a permanently connected braid with wires and an electrical connector that are not separable from the sensor. Damage to the wiring harness or removal of the wiring harness or electrical connector may impair the functionality of the sensors.
Prevent dirt, grease and other substances from coming into contact with the sensors.
Do not use solvents to clean sensors.
Do not throw or hit the sensors.
Since the sensors are mounted in the exhaust manifold or tailpipe, they are prone to burn-in, making them very difficult to remove on a cold engine.
Replacement of oxygen sensors (O2S) produce as follows:
To eliminate the possibility of damaging the sensors, run the engine for 1–2 minutes, then turn it off. Removing the sensors is now easier, but care must be taken to avoid burning yourself on the hot exhaust manifold and tailpipe.
Turn off the ignition and disconnect the ground wire from the battery.
If it is necessary to remove the secondary sensor, raise the vehicle on a lift.
Figure 7.17. Location of the primary oxygen sensor on bank 2 on models since 2001
The primary sensor can be replaced without raising the vehicle (figure 7.17).
Disconnect the electrical connector located on the oxygen sensor wires.
Figure 7.18. Location of the secondary oxygen sensor on bank 1 on models since 2001
Remove the sensor from the exhaust manifold or tailpipe (figure 7.18). Use a socket wrench to remove the sensor.
Apply a non-stick compound to the sensor threads to make it easier to remove the sensor later. The threads of the new sensor are already coated with a non-stick compound. Screw in the sensor and tighten it securely.
Connect the sensor electrical connector.
Lower the car.
Install the sensor in the reverse order of removal.