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Background knowledge: The role of the oxygen sensor is to measure the oxygen content in the engine exhaust to correct the fuel injection volume, so that the engine can obtain the best air-fuel ratio. In the OBD fault code, you will often see the statement of which oxygen sensor in the first row. The first row refers to the row where cylinder 1 is located, and the remaining row is the second row. Regardless of the row, the first sensor always refers to the upstream oxygen sensor (front oxygen), and the second sensor always refers to the downstream oxygen sensor (rear oxygen). The electronic control unit (ECU) continuously monitors the heating oxygen sensor heater to ensure that there is no open circuit, short circuit, or excessive current consumption. If the current consumption exceeds the calibration limit, or an open circuit or short circuit is detected, this fault code will appear. The causes of the fault include open circuit of the oxygen sensor heater voltage circuit or open circuit of the heater ground wire circuit, signal crossing caused by oil or moisture in the connector, failure of the oxygen sensor itself, failure of the electronic control module (PCM or ECM), etc. After troubleshooting, the fault code needs to be cleared. When clearing the code, it should be carried out strictly in accordance with the fault code clearing method specified for the specific vehicle type, and the negative grounding wire of the battery must not be directly removed in order to clear the fault code. Otherwise, it is likely to cause problems in the following two situations: First, it caused the control center computer of some models to lose normal records. I believe everyone understands that many models of car computers have automatic memory functions. After the ground wire of the negative battery is easily removed, the engine running in the random access memory will be lost. Empirical data, which causes the performance of the car to be average for a long period of time after maintenance, or after a period of driving, a fault code that has been cleared appears again; Second, it will also cause the loss of certain functions. For example, the audio lock is one of the more common examples. At this time, it is necessary to decrypt the audio system through a troublesome repair procedure to restore the original audio system. Function.

A 2012 Honda Accord 2.0 sedan has a mileage of about 30,000 km. The engine idling jitter is serious, acceleration is weak, and the engine fault light is always on. The air-fuel ratio sensor is malfunctioning. 1. Repair process 1. Use HDS to detect, the fault code read is P2A00, air-fuel ratio (A/F) sensor S1 circuit range/performance problem, record and clear the fault code and test drive, the fault remains. So it was decided to start with the air-fuel ratio sensor to troubleshoot the fault according to the prompt of the fault code. 2. Connect HDS for road test and record relevant snapshot data at the same time. According to the data, the air-fuel ratio sensor signal of this car fluctuates too frequently around 0 mA, and the signal voltage of the oxygen sensor has been around 0V (indicating that the mixture concentration is always leaner). It is inferred from this that the air-fuel ratio sensor signal is abnormal, so that the engine control module (PCM) incorrectly controls the concentration of the mixture, resulting in engine idling jitter and weak acceleration. 3. The possible reasons for the abnormal signal of the air-fuel ratio sensor are: the air-fuel ratio sensor and its wiring failure; electromagnetic signal interference. 4. Electromagnetic signal interference usually comes from electrical appliances and auxiliary parts installed later. After careful inspection, it was found that the car was not equipped with electrical appliances that easily cause electromagnetic signal interference, such as atmospheric headlights, the generator was working normally, and the four spark plugs were all original parts, thereby eliminating the possibility of electromagnetic interference. 5. Visual inspection of the circuit of the air-fuel ratio sensor revealed no damage to the wiring harness, poor connection of the wire connector, and oxidation of the terminal. It seems that the failure is caused by the failure of the air-fuel ratio sensor itself. 3. Case suggestions For vehicles with recorded fault codes, the corresponding fault codes should be tested according to the methods specified in the maintenance manual after the repair, and then confirm whether the corresponding fault codes have passed the test through the OBD status list of HDS. If it fails the test, it may malfunction soon The code will still appear. The test method of fault code P2A00 is as follows: (1) Make the engine coolant temperature higher than 70 ℃. (2) For automatic transmission models, put the shift lever in the "D" position; for manual transmission models, put the shift lever in the 3rd or 4th gear. (3) Continue to drive for 5 minutes at a speed of 40 km/h-88 km/h. (4) After driving stably at a speed of 88 km/h-120 km/h for 10 seconds, decelerate (throttle valve is completely closed) for 5 seconds, and the test is completed.