“In the waveform test method, a jumper wire or probe is connected to the sensor signal terminal, and the other measuring wire is grounded.
In the waveform test method, a jumper wire or probe is connected to the sensor signal terminal, and the other measuring wire is grounded.
(1) The waveform test method is connected to the sensor signal terminal with a jumper wire or probe, and the other measuring wire is grounded. Turn on the ignition switch, the engine does not run, and measure the signal voltage output by the sensor. Start the engine, and then observe the voltage drop during the warm-up process, and also observe the change of its resistance value, but the sensor wiring must be unplugged. (2) Waveform analysis engine coolant temperature sensor, usually when the car is cold, its voltage should be 3 to 5V (fully cold), and then gradually decrease to about IV at normal operating temperature as the engine runs.
The deterministic measure of the magnitude of the DC signal. At any given temperature, a good sensor must produce a stable feedback signal. An open circuit of the engine coolant temperature sensor circuit will cause an upward spike in the voltage waveform (to the reference voltage value), and a short circuit of the engine coolant temperature sensor circuit will produce a downward spike (to the ground value). When the temperature sensor fails, the waveform is not smooth, and there are glitches down.
The glitch indicates that the sensor voltage signal is discontinuous, and the potentiometer is short-circuited or intermittently disconnected. The reason for the influence of the waveform is that the battery voltage is not above 12V; the air filter is blocked; the intake pipe is leaking; the cooling fan is insufficient; the sensor reference voltage is abnormal; the connector plug is loose; the internal circuit of the sensor is open or short-circuited; the output voltage of the control unit Abnormal; bad grounding.
The reason for the abnormal waveform of the coolant temperature sensor may be that the radiator is overheated; the coolant level is insufficient; the expansion tank or the water pipe is leaking; the sensor power supply voltage is not 5V; the output voltage of the control unit is abnormal; and the grounding is poor. The reason for the abnormal waveform of the intake air temperature sensor may be that the air filter is blocked; the reference voltage or resistance cannot correspond to the temperature; the connection line is loose; the sensor voltage is not 5V; the output voltage of the control unit is abnormal and the grounding is poor.