The diagnostic idea of ​​sensor signal voltage is too high and the voltage is too low.

The diagnostic idea of ​​sensor signal voltage is too high and the voltage is too low.

01

Sensor signal voltage is too high failure

In automotive circuit maintenance, you can often encounter a fault code about the signal voltage of the sensor. According to the sensor’s power supply circuit, it can be found that if the negative opening of the sensor, the sensor lost the negative electrode and the output signal voltage has always been 5V. According to the fault monitoring logic of the engine computer, the effective signal voltage range of the computer monitoring sensor is 0.2 to 4.8V. More than 4.8V computers will report a fault code with a high signal voltage. Therefore, when the sensor loses the negative signal, the voltage becomes 5V, and the computer will leave a fault code (the signal voltage is too high).

For this type of failure, you need to check the negative electrode of the sensor. If the negative electrode line does not open, you also need to check whether the signal line is short -circuited to the positive electrode. If not, it is generally damaged by the sensor.

传感器信号电压过高、电压过低故障的诊断思路

Another situation is that multiple sensors report the fault code at the same time (the signal voltage is too high). This situation is generally a public negative opening road. According to the author’s many years of maintenance experience, in addition to the line opening, more possibilities are that the negative lines inside the computer are burned. The reason for the burning of the negative line may be that the damage of a sensor causes the negative electrode line to the 12V voltage. For example, the high failure rate is the short circuit inside the oxygen sensor to short the signal negative short circuit to the 12V power supply, thereby burning the internal line of the computer. Another situation is the misunderstanding of the repairman. The use of high -power test lights to connect the positive pole to verify whether the negative electrode of the sensor is good, so that the operation is easy to damage the computer. As shown in the figure below is the maintenance diagram burned by the internal negative line of the computer.

传感器信号电压过高、电压过低故障的诊断思路

The maintenance map of the internal negative line of the computer

02

Sensor signal voltage is too low failure

In the same way, if the sensor loses the positive electrode, the output voltage of the sensor has always been 0V, then the computer will record a fault code (the sensor signal voltage is too low). When repairing such faults, the power supply of the sensor should be detected normally. If it is normal, the signal line of the sensor will be tested for short circuits on the negative electrode. If there is no problem, it can basically be judged that it is the failure of the sensor itself.

If multiple sensors report the fault code at the same time (the signal voltage is too low), it should be the short circuit of the public positive electrode to the ground (5V voltage to the ground short circuit will not burn the computer, just find a short circuit place to recover), the short circuit point may be the short circuit point may be the short circuit point). A sensor may also be the plug or line itself. I recommend a simple detection method here: first find a better measurement sensor, connect the power supply of the multimeter and the sensor. At this time, the multimeter should display 0V, and then unplug the sensor that may fail. While unplugging the sensor, pay attention to observe whether the plug oxidation is oxidized. Until the display of 5V display 5V, it represents the failure caused by the short circuit inside the sensor. If you have not recovered after all are out, it may be the failure of the line. At this time, you need to be patient.

Is the 12V power supply of the engine computer? The answer is no, because according to 12V power supply logic, only the engine and computer power supply is intact, the main relay is closed, and the engine computer can communicate. The fault code is read here, which means that the communication is good, so it has nothing to do with 5V and 12V power supply. Essence

As shown in the figure below, the circuit of a Shanghai GM Cruz engine and computer can be seen. You can see that the vehicle engine control system has two sets of 5V power supply, of which a set of 5V power supply, air -conditioning pressure sensor and air -conditioning pressure sensor and air conditioner pressure sensor and air conditioner pressure sensor are shared. The crankshaft position sensor shares a set of 5V power supply. In the general model, if a 5V power supply to the ground is short -circuit, the computer will leave a separate failure code, for example: “5V 1 reference voltage”. This fault code refers Short -circuit to the ground.

Shanghai Universal Cruz engine computer circuit

Product Recommendation: 12v sensor

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