Engine oxygen sensor fault diagnosis and maintenance plan

In electronically controlled gasoline injection engines, the oxygen sensor used for closed-loop control of the fuel system is an important electronic component that monitors the oxygen content in the exhaust gas and feeds back the voltage signal to the ECU to control the air-fuel ratio to 14.7. At the same time, it is also a representative alarm component for multiple fault signals.

1. Oxygen sensor fault diagnosis

From the characteristic curve of the zirconia sensor, we can see that when the air-fuel ratio is maintained at 14.7, the signal reference voltage is 0.4-0.5V. When the air-fuel ratio is less than 14.7, its voltage gradually increases to 0.8-1V, indicating that the mixture is too rich. When the air-fuel ratio is greater than 14.7, its voltage gradually decreases to about 0.2V, indicating that the mixture is too lean. This is an important basis for oxygen sensor diagnosis, and its diagnostic method is:

1. Run the engine at 2500r/min for 2 minutes, preheat the sensor, unplug the sensor plug (pay attention to the plug angle position for sensors with heating wires), use a multimeter to measure the feedback voltage, and check the number of voltmeter pointer swings within 10 seconds. If it is less than 8 times, preheat the sensor again and check the number of pointer swings within 10 seconds. If it swings more than 8 times, it is normal. If it is still less than 8 times, continue as follows:

2. Disconnect the sensor harness plug and measure the feedback voltage.

1) When the voltage is greater than 0.45V, disconnect the vacuum tube somewhere on the intake pipe. If the voltage is still greater than 0.45V, it means the sensor is damaged. If it is less than 0.45V, it means the mixture is too rich and the fuel, intake or control system should be checked.

2) When the voltage is less than 0.45V, unplug the water temperature sensor and connect a 4-8KΩ resistor. If the voltage is still less than 0.45V, it means the sensor is damaged. If it is higher than 0.45V, it means the mixture is too lean.

The common zirconia sensor failure is that the surface is covered by lead or carbide, which makes the gas impermeable and the oxygen ions unable to diffuse, resulting in failure. When the fault light alarms and the sensor fault is read, it is necessary to diagnose it, because the oxygen sensor alarm does not necessarily mean that the sensor is faulty, and its alarm signal is also affected by the following factors.

1. Working condition of ignition system;

2. Sealing performance of the air intake system;

3. Is the exhaust system blocked?

4. The working condition of the injector;

5. The oil pressure of the oil supply system.

Therefore, during engine maintenance, once the oxygen sensor alarm signal appears, the faulty part should be comprehensively analyzed, judged, and replaced through a computer and human brain, and repaired reasonably.

2. Detection of the working condition of the ignition system

Perform routine inspections on the microcomputer controlled ignition system with or without distributor. The inspection items are spark energy, spark plugs, high voltage wires, ignition timing, ignition advance angle, etc. When checking the ignition advance angle with an ignition timing lamp, connect the red fish clamp to the positive pole of the battery, the black fish clamp to the negative pole of the battery, and the high voltage sensor to the high voltage wire of one cylinder. The timing lamp is aimed at the ignition timing mark of the front pulley of the engine. When the engine speed increases, the ignition advance angle should increase. Use a hammer or a wrench to hit the knock sensor fixing screws or the cylinder head, and the ignition advance angle should be significantly delayed.

3. Check the sealing performance of the intake system

Connect a vacuum gauge to the appropriate part of the intake pipe. When the engine is idling (500-600r/min), the vacuum degree of the intake pipe should be within the range of 57.33-70.66Kpa based on the sea level. Otherwise, repair the leaking part of the intake system. When idling, the vacuum gauge pointer gradually drops to zero, indicating that the exhaust system is blocked. The change of the vacuum gauge pointer can also detect the valve sealing and ignition performance.