Throttle Position Sensor: Description and Operation

Throttle Position Potentiometer:

PURPOSE
The Throttle Position (TP) Sensor supplies throttle-angle information to the Digifant control module. The control module uses this information for:

^ Idle air control
^ Deceleration fuel shut-off
^ Wide-open throttle enrichment


CONSTRUCTION
The throttle position sensor consists of a housing mounted to the Throttle Body 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 ECM
Terminal # 3 = Throttle position signal (varies from approx. 0.5V at idle to 4.5V at full load)

OPERATION AND SIGNAL
The throttle position sensor detects the throttle angle by scanning a resistance track on the sensor. The Digifant control module is informed of the entire range of throttle valve movement from closed throttle to wide-open throttle.

The fuel injection Engine Control Module (ECM) 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 ECM which uses the remaining voltage as the throttle position signal.

Depending on where the contacts are located on the carbon track (terminals 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 ECM. The resistance is at its maximum when the throttle is in the idle position.

On vehicles equipped with a manual transmission, a dash pot is used to delay the closing of the throttle valve just before idle. The delay allows the engine to burn the fuel that may be present during the transition from normal engine operation to deceleration fuel shut-off. Its purpose is to help reduce exhaust emissions.