Throttle position sensor (potentiometer)

The purpose of this test is to examine the operation of a Throttle Position Sensor (TPS) potentiometer based on output quality and response time in relation to throttle position.

How to perform the test

View connection guidance notes.

1. Use manufacturer's data to identify the sensor output circuit.
2. Connect PicoScope Channel A to the sensor output circuit.
3. Turn ignition on engine off.
4. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
5. Start the scope to see live data.
6. Carefully and slowly fully open and close the throttle.
7. With your waveform on screen stop the scope.
8. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Waveform notes

This known good waveform has the following characteristics:

• A constant, unbroken, voltage output at around 0.7 V, with the throttle at its idle position.
• As the throttle moves from its idle position, at around 0.5 s, the output progressively increases with increasing throttle opening.
• With the throttle at its fully open position, the output is around 3.7 V. The output is maintained whilst the throttle remains in the fully open position.
• As the throttle moves back from its fully open position, the output voltage progressively decreases.
• The voltage output returns to a constant 0.7 V with the throttle back at its idle position.
• There is no drop-out, noise, or hash on the waveform.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select Throttle position sensor TPS.

Further guidance

A throttle position sensor signals the position of the throttle valve to the Engine Control Module (ECM).

Throttle potentiometers are generally carbon track type units mounted directly onto the throttle butterfly spindle. They are a three-wire device with a reference 5 V supply, output signal and earth terminals.

Some manufacturers combine the potentiometer with the throttle actuator motor. Whether combined or separate components, their function remain the same.

As the throttle position is critical to engine control, the normal operating output range of the TPS is within some margin of the earth and reference 5 V supply voltages. For example, from around 0.5 V to around 4.5 V. This provides a means for the ECM to check the integrity of the sensor and circuits: a voltage below or above this expected output range will indicate an open circuit, a short to earth, or a short to the reference 5 V supply. Either of these outcomes will cause the ECM to register a sensor fault.

Faulty Throttle Potentiometer – Symptoms

• Malfunction Indicator Lamp (MIL) illumination.
• Poor/erratic starting.
• Stalling, hesitation or other drivability.
• Incorrect fuel trims causing possible fuel consumption or emissions issues.

Faulty Throttle Potentiometer – Causes

• Mechanical damage caused by heat and vibration.
• Internal short circuits caused by fluid contamination and humidity.
• Contact and external circuit damage.
• Frictional wear of moving parts.

GT029