The diagnosis of the fault that the sensor signal voltage is too high or too low

01

The sensor signal voltage is too high.​

In the maintenance of automobile circuit, the fault code about the overvoltage of sensor signal is often encountered. According to the power supply circuit of the sensor, it can be found that if the negative electrode of the sensor is open, the sensor loses the negative electrode and the output signal voltage is always 5V. According to the fault monitoring logic of engine computer, under normal circumstances, the effective signal voltage range of computer monitoring sensor is 0.2 ~ 4.8V. Above 4.8V, the computer will report the signal voltage is too high fault code. So when the sensor loses its negative signal and the voltage changes to 5V, the computer will leave a fault code (signal voltage is too high).

For this type of fault, check the negative pole of the sensor. If the negative pole line is not open, check whether the signal cable is short-circuited to the positive pole. If not, the sensor is damaged.

There is also a situation where multiple sensors at the same time reported fault code (signal voltage is too high). This situation is generally a public negative circuit. According to the author's many years of maintenance experience, in addition to the open circuit, more likely is the computer inside the negative wire burned off. The reason for the negative wire burning may be that a sensor is damaged and the negative wire is short-circuited to the 12V voltage. For example, the high failure rate is that the short circuit inside the oxygen sensor shorted the signal negative to the 12V power supply, thus burning the internal circuit of the computer. There is also a case of repairman's operation, the use of high-power test light connected to the positive electrode to verify whether the negative electrode of the sensor is good. such operation is easy to damage the computer.

02

The sensor signal voltage is too low.​

Similarly, if the sensor loses its positive terminal, the output voltage of the sensor will always be 0V, and the computer will record a fault code (sensor signal voltage is too low). When repairing this kind of fault, we should first detect whether the power supply of the sensor is normal, if normal, then detect whether the signal line of the sensor is short circuit to the negative pole. If there is no problem, then you can basically judge the fault of the sensor itself.

If multiple sensors report fault code at the same time (signal voltage is too low), it should be a public positive to ground short circuit (5V voltage to ground short circuit will not burn the computer, just need to find the place of the short circuit to recover), the short circuit point may be a sensor, it may also be the plug or the line itself. A simple method is recommended: find a sensor that is easy to measure, connect the multimeter to the power supply of the sensor, the multimeter should display 0V, and remove the sensor that may be faulty. When removing the sensor, check whether the plug is oxidized by water. If the multimeter displays 5V, the fault is caused by a short circuit inside the sensor. If all unplug is not recovered, it may be the fault of the line, at this time need to be patient detection.

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

​a Shanghai General Cruze engine computer circuit, we can see that the car engine control system has two groups of 5V power supply, in which the intake and exhaust camshaft position sensor and air conditioning pressure sensor share a group of 5V power supply, air conditioning pressure sensor and crankshaft position sensor share a group of 5V power supply. In general models, if a 5V power supply circuit is short to ground, the computer will leave a single fault code, such as "5V 1 reference voltage". This fault code means that the voltage of the 5V 1 line is too low, which means that the circuit is short to ground.

01 The sensor signal voltage is too high.​ In the maintenance of automobile circuit, the fault code about the overvoltage of sensor signal is often encountered. According to the power supply circuit of the sensor, it can be found that if the negative electrode of the sensor is open, the sensor loses the negative electrode…

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