Note: all described vehicles are equipped with two oxygen sensors located in front of the catalyst and behind it.
1. The oxygen sensor records the amount of oxygen remaining in the exhaust after combustion of the air-fuel mixture. The oxygen remaining in the exhaust reacts with the sensor element, and thus generates a pulse, the voltage of which lies within 0.1 (increased oxygen content, lean mixture) - 0.9 V (low oxygen content, rich mixture). The upstream oxygen sensor is located in the exhaust system in front of the converter. The PCM constantly monitors the pulses of the upper sensor, on the basis of which the optimal pulse width of the injectors is maintained and, thus, the optimal air-fuel mixture ratio is ensured. The mixture, which has a ratio of 14.7: 1, is optimal for ensuring low exhaust toxicity and maximum fuel economy at the highest operating conditions. characteristics of the power unit. Thus, the PCM constantly maintains the specified mixture ratio based on pulses from the oxygen sensor.
2. Based on pulses from the lower oxygen sensor (located in the exhaust system behind the catalytic converter) The RSM does not determine the need to adjust the air-fuel mixture ratio. The operating principle of the lower oxygen sensor is similar to the operating principle of the upper sensor. Based on the signals from the lower sensor in the PCM, the efficiency of the catalytic converter is determined. The change in pulse amplitude of the lower sensor is slower than the change in signal amplitude of the upper oxygen sensor because the exhaust gases passing through the catalytic converter contain less oxygen.
3. Not warmed up to operating temperature (approximately 318°C), the oxygen sensor does not generate pulses. During the period before the sensor heats up, the PCM directly controls the fuel supply. In this case, the sensor signal does not determine the amount of oxygen in the exhaust gases. The fuel supply to the PCM is controlled based on signals from other sensors of the control system using a built-in program. All oxygen sensors have a heating element that is connected to the battery through a fused power circuit. When voltage is applied, the sensor warms up to operating temperature in the shortest possible time.
4. Four factors affect the operation of the oxygen sensor:
- A) Electrical - the clarity of transmission of low voltage pulses depends on the condition of the connectors, which should be inspected first if the oxygen sensor malfunctions.
- b) Possibility of air circulation - the sensor functions when air circulates in its housing.
- When removing, installing or replacing a sensor, make sure that its air passages are clear.
- With) Creation of operating temperature - the PCM cannot record the sensor signal until it warms up to operating temperature, approximately 318°C. This factor must be taken into account when evaluating sensor performance.
- d) Use of unleaded gasoline - To ensure proper functioning of the sensors, the vehicle must be fueled with unleaded gasoline only.
5. The PCM can detect several causes of sensor malfunction. At the same time, the corresponding diagnostic codes are registered in the microprocessor memory, defining the specifics of the problem (see subsection 2). If the sensor fails, its pulses are neglected and the RSM goes into direct fuel supply control mode, as described above.
Replacement
6. Because the exhaust pipe contracts when cooled, it may be difficult to loosen the oxygen sensor torque when the engine is cold. To prevent damage to the sensor when unscrewing, first start the engine and turn it off after two minutes. Be careful not to get burned during the following procedure. Considering the factors listed below, you should handle the sensor with care when touching it.
- A) The oxygen sensor has a shank and connector that should not separate when removed. Damage or separation of the shank or electrical connector may adversely affect the further operation of the sensor.
- b) Keep grease, dirt, and other contaminants away from the connector and open end of the sensor.
- With) When cleaning the oxygen sensor, do not use solvent.
- d) Handle the sensor with care and do not allow it to fall.
- e) Do not try to repair the sensor wiring - if it is damaged, it must be replaced.
7. When replacing the downstream oxygen sensor, the vehicle must be raised and vertical supports installed.
8. The upstream oxygen sensor can be replaced without lifting the vehicle.
9. Disconnect the connector from the sensor (see illustrations).
11.9a. Location of the upstream oxygen sensor, whose signals reflect engine efficiency
11.9b Location of the downstream oxygen sensor, the signals of which indicate the efficiency of the catalytic converter
10. Using a suitable wrench or special socket, unscrew the sensor from the exhaust pipe.
11. To facilitate subsequent unscrewing, an anti-seize compound must be applied to the sensor threads. Typically, a new sensor comes with anti-seize compound applied to the threads. If not, coat the threads with compound.
12. Install and tighten the sensor securely.
13. Connect the connector to the sensor and lower the vehicle.