Tip & How-To about Mercedes-Benz E-Class
1.3) TPS - Throttle Position Sensor
What is it? This is an electrical device that detects the position of the throttle plate.
Where is it located? The TPS is found on the exterior of the throttle body on the opposite end of the throttle shaft to the accelerator linkage arm. It usually consists of a small black plastic unit with an electrical connector attached to it.
How does it work? The TPS is a variable resistor madeup of an arc shaped carbon track with an applied voltage of 0 to 5 volts along its length and a sliding contact that picks up the voltage at any point along it. The device has three electrical connections, two provide the voltage range along the carbon track and the third (most often the middle connection) sends a voltage to the ECU in accord with the position of the sliding contact point on the arc. This siding contact arm is attached to the end of the throttle shaft. As the throttleshaft rotates, opening and closing the throttle plate, the sliding contact sweeps up and down the carbon track providing voltage readings to the ECU; 0 volts for closed to 5 volts for fully open.
When the engine is at idle the TPS output should signal the ECU that the throttle is closed (low volts) and therefore the ECU should either open the Idle Air Control (IAC) valve or (on some engines) engage the idle speed control motor to maintain the engine idle speed. Sometimes a micro contact switch on the throttle body exterior associated with the throttle shaft is used to detect and confirm when the throttle plate is fully closed.
NEXT 1.3b) TPS faults and how to fix
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