How to use an oscilloscope to measure the signal of the accelerator pedal sensor

The car's accelerator pedal position sensor converts the amount (angle) of pedal depression into a voltage signal, thereby providing the engine control unit with a signal of the actual opening angle of the accelerator pedal.

Its working principle is that the engine control unit supplies 5V voltage to the accelerator pedal position sensor, and the sensor sends two voltage signals reflecting the accelerator pedal position to the engine control unit. When the engine is started, the accelerator pedal is not stepped on or is lightly stepped on, and the throttle valve opens to a fixed position under the control of the preset program, that is, the engine control unit performs startup control according to this signal. There are two types of accelerator pedal position sensors: linear type and Hall element type.

New engine electronic control systems are increasingly using fully electronic throttles, which require an accelerator pedal position sensor. This sensor converts the driver's operation into a voltage signal, which is sent to the engine computer. The engine computer then outputs a signal to drive the throttle motor, ultimately achieving control of the engine power.

The accelerator pedal position sensor is designed in the engine room and is connected to the accelerator pedal by a cable. The sensor consists of two potentiometers, which output two signals. The two signals are sent to the engine computer at the same time. The engine computer monitors the two voltage signals at the same time. If the throttle opening expressed by the two voltage signals is consistent, the command is executed; if not, the engine acceleration is restricted for protection.

Let's see how to use an oscilloscope to measure the car accelerator pedal sensor signal:

Connect a BNC to banana cable to channel 1 of the oscilloscope. Connect a black alligator clip to the black connector (negative) of the test lead and connect it to an appropriate ground point. Connect a piercing needle to the positive terminal and pierce one of the potentiometer leads in the accelerator pedal sensor plug.

Connect a BNC to banana cable to channel 2 of the oscilloscope. Connect a needle to the positive terminal and pierce the other potentiometer connection wire in the accelerator pedal sensor plug. If you have a suitable automotive lead wire, you can use it instead of the piercing method.

After the connection is complete, set the channel attenuation ratio of the oscilloscope channel 1 and 2 to 1X, and the vertical range to 1V or 500mV. If the oscilloscope has high and low pass functions, you can turn on the low pass 30KHz and set the time base to 500ms. Some oscilloscopes have built-in car package software, which can be set with one click.

After setting, start the car and press the accelerator pedal. Under normal circumstances, the oscilloscope will display the accelerator pedal sensor signal waveform.

The accelerator pedal position sensor is a potentiometer type sensor. It receives two reference voltages from the powertrain control module (PCM), has two ground wires, and two signal wires (the signal wires send a varying voltage to the PCM that is related to the accelerator pedal position). The signal voltage sent back to the PCM will vary from car to car, but will never be higher than 5V.