Throttle Position Sensor: Description and Operation

Throttle Position Sensor:

PURPOSE
The throttle position sensor supplies the fuel injection ECU with a linear voltage signal based on throttle valve position. The injection ECU sends a modified signal to the ignition ECU.

The fuel injection ECU uses the signal for full load enrichment and idle functions.

The ignition ECU uses the signal to adjust timing.

LOCATION
On the throttle housing.

Potentiometer In Throttle Position Sensor:

CONSTRUCTION
The throttle position sensor consists of a housing mounted to the throttle valve shaft, a potentiometer fitted with two contacts running on two carbon tracks and a wiring connector terminal. The sensor is not adjustable.

TERMINAL IDENTIFICATION
Terminal #1 = To ground
Terminal #2 = 5 volt supply signal from Fuel injection ECU
Terminal #3 = Throttle position signal (varies from approx. 0.5V at idle to 4.5V at full load)


OPERATION AND SIGNAL
The fuel injection ECU supplies the throttle position sensor with a 5 volt supply signal. This signal passes through the carbon track, over the two contacts and returns via the second carbon track to the ECU which uses the remaining voltage as the throttle position signal.

Depending on where the contacts are located on the carbon track (contacts move with the throttle valve), the current must pass through a larger or smaller section of the track. This increases or decreases the circuit resistance, affecting the voltage returning to the ECU. The resistance is at its maximum when the throttle is in the idle position.