How to detect the three terminals of the throttle position sensor?

The linear throttle position sensor can tell the electronic control module (ECM) the accurate throttle opening.

Most modern management systems will use this sensor, which is installed on the throttle butterfly drive shaft. It is a three-wire device with a 5-volt power line, a grounding line and a variable signal output line at the middle pin. This signal output is very important to the performance of the car. Any "blind spot" in the sliding area of internal carbon rail will lead to "stagnation" and "slow response" This discontinuity can be seen from the oscilloscope waveform, and the operator can mark any fault area indicated by the output voltage within his working range.

A good throttle potentiometer should show that the voltage is very small when the throttle is closed, gradually rises when the throttle is opened, and returns to the initial value when the throttle is closed. Although the voltage of most throttle position sensors is defined by the manufacturer, most of them are not adjustable.

Let's talk about the connection and setting method of oscilloscope first.

Connect the BNC- banana head cable to the first channel of the oscilloscope. The red banana head is connected to the signal output end of the sensor with a needle, and the black banana head is connected to the ground with a crocodile clip. Oscilloscope channel attenuation ratio is set to 1X, vertical gear is set to 500mV, and time base can be set to1s. In order to prevent burr interference, low-pass filtering can be turned on, and some oscilloscopes also support one-button setting.

Turn on the ignition switch, the engine is not running, slowly let the throttle from the closed position to the fully open position, and then return to the throttle closed position again. Repeat this process several times slowly.

Some vehicles have two throttle position sensors. One for engine control and the other for transmission control. The signal from the engine throttle position sensor corresponds to the operation of the transmission throttle position sensor. The signals of the two throttle position sensors are opposite and check each other. We call this design pattern "redundant" design.