On cars the system of onboard diagnostics OBD-II in a control system of the engine which has feedback between the sensor of oxygen and the control unit of the engine (PCM) is installed. It is reached due to installation of primary sensor of oxygen or the sensor of fuel-air 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 in size. On the basis of these data the control unit of the engine changes time of opening of nozzles and a ratio of fuel in fuel-air mix. In order that there was a full combustion of gas mixture and in the fulfilled gases there were no harmful substances, 1 part of fuel has to 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
Do not mix sensors of oxygen and fuel-air mix. They are similar on appearance, but work differently and have various operational characteristics.
Like the oxygen sensor, the sensor of fuel-air mix transforms information to the output tension transferred to the control unit of the engine. The size of a signal is proportional to the air/fuel mix relation in a stream of the fulfilled gases. The sensor of fuel-air mix changes output 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 fuel-air mix begins to work normally only after warming up for what install heaters on sensors.
At service of sensors take the following precautionary measures:
Sensors of oxygen and fuel-air mix have constantly connected braid with wires and the electric socket which are not separable from the sensor. Damage of a braid with wires or its removal or the electric socket can break operability of sensors.
Exclude hit of dirt, lubricant and other substances on sensors.
Do not use solvents for cleaning of sensors.
Do not throw and do not strike sensors.
As sensors are installed in a final collector or an exhaust pipe, they burn therefore it is very difficult to remove them on the cold engine.
You make replacement of sensors of oxygen (O2S) as follows:
To exclude probability of damage of sensors, launch the engine for 1–2 min., then switch off it. Removal of sensors is facilitated now, however at the same time it is necessary to be careful not to burn about a hot final collector and an exhaust pipe.
Switch off ignition and disconnect a wire of "weight" from the rechargeable battery.
If it is necessary to remove the secondary sensor, lift the car on the elevator.
Fig. 7.17. An arrangement of primary sensor of oxygen on the block 2 on models since 2001
Primary sensor can be replaced, without lifting the car
Disconnect the electric socket located on oxygen sensor wires.
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
. For a reversing of the sensor use a cutting cap key.
Apply antiprigarny structure which will facilitate the subsequent otvorachivaniye of the sensor on a sensor carving. The carving of the new sensor is already covered by antiprigarny structure. Screw the sensor and reliably tighten it.
Connect the electric socket of the sensor.
Lower the car.
You carry out installation of the sensor to the sequences, the return to removal.