On cars the system of onboard diagnostics of OBD-II in a control system of the engine which has feedback between the sensor of oxygen and the control unit the engine (PCM) is established. It is reached at the expense of installation of the primary sensor of oxygen or the sensor of a toplivovozdushny mix before catalytic converter and the secondary sensor of oxygen behind converter. Depending on the content of oxygen in the fulfilled gases the sensor of oxygen induces tension corresponding on size. On the basis of these data the control unit the engine changes time of opening of nozzles and a fuel ratio in a toplivovozdushny mix. In order that there was a complete combustion of gas mixture and in the fulfilled gases there were no harmful substances, 1 part of fuel should fall on 14,7 weight parts of air.

Defining composition of the fulfilled gases before and after converter, PCM defines efficiency of converter.

Fig. 7.16. An arrangement of sensors of oxygen on models since 2001: 1–electric sockets; 2–oxygen sensor (block 2, sensor 2); 3–oxygen sensor (block 1, sensor 2)

Primary (in the direction of the fulfilled gases) the sensor of oxygen is located in a final collector or in an exhaust pipe, and secondary — behind catalytic converter (fig. 7.16) .

PREVENTION Do not mix sensors of oxygen and a toplivovozdushny mix. They are similar on appearance, but work differently and have various operational characteristics.

Like the oxygen sensor, the sensor of a toplivovozdushny mix transforms information to the target tension transferred to the control unit by the engine. The size of a signal is proportional to the relation of a mix of air/fuel in a stream of the fulfilled gases. The sensor of a toplivovozdushny mix changes target tension from 3,3 to 3,0 in depending on an oxygen proportion in a stream of the fulfilled gases. Like the oxygen sensor, the sensor of a toplivovozdushny mix starts to work normally only after warming up for what on sensors establish heaters.

At service of sensors accept the following precautionary measures:

Sensors of oxygen and toplivovozdushny mix have constantly connected braid with wires and the electric socket which are not separable from the sensor. Braid damage with wires or its removal or the electric socket can break operability of sensors.

Exclude hit of dirt, greasing and other substances on sensors.

Do not use solvents for cleaning of sensors.

Do not throw and do not strike sensors.

As sensors are established in a final collector or an exhaust pipe, they burn, therefore they are very difficult for removing on the cold engine.

Replacement of sensors of oxygen (O2S) make as follows:

To exclude probability of damage of sensors, start up the engine on 1–2 mines, then switch off it. Removal of sensors is facilitated now, however thus it is necessary to be careful not to burn about a hot final collector and an exhaust pipe.

Switch off ignition and disconnect a "weight" wire from the storage battery.

If it is necessary to remove the secondary sensor, lift the car on the lift.

Fig. 7.17. An arrangement of the primary sensor of oxygen on the block 2 on models since 2001

It is possible to replace the primary sensor, without lifting the car (fig. 7.17) .

Disconnect the electric socket located on wires of the sensor of oxygen.

Fig. 7.18. An arrangement of the secondary sensor of oxygen on the block 1 on models since 2001

Turn out the sensor from a final collector or an exhaust pipe (fig. 7.18) . For a reversing of the sensor use a cutting cap key.

Put on a sensor carving antiprigarny structure which will facilitate the subsequent otvorachivaniye of the sensor. The carving of the new sensor is already covered with antiprigarny structure. Screw the sensor and reliably tighten it.

Connect the electric socket of the sensor.

Lower the car.

Installation of the sensor carry out to sequences, return to removal.