The TPS is mounted on the throttle body and converts the throttle valve angle into an electrical signal. As the throttle opens, the signal voltage increases.
The ECM uses throttle valve position information to know:
• engine mode: idle, part throttle, wide open throttle.
• switch off AC and emission controls at Wide Open Throttle (WOT).
• air-fuel ratio correction.
• power increase correction.
The basic TPS requires three wires. Five volts are supplied to the TPS from the VC terminal of the ECM. The TPS voltage signal is supplied to the VTA terminal. A ground wire from the TPS to the E2 terminal of the ECM completes the circuit.
At idle, voltage is approximately 0.6 - 0.9 volts on the signal wire. From this voltage, the ECM knows the throttle plate is closed. At wide open throttle, signal voltage is approximately 3.5 - 4.7 volts.
Inside the TPS is a resistor and a wiper arm. The arm is always contacting the resistor. At the point of contact, the available voltage is the signal voltage and this indicates throttle valve position. At idle, the resistance between the VC (or VCC terminal and VTA terminal is high, therefore, the available voltage is approximately 0.6 - 0.9 volts. As the contact arm moves closer the VC terminal (the 5 volt power voltage), resistance decreases and the voltage signal increases.
Some TPS incorporate a Closed Throttle Position switch (also called an idle contact switch). This switch is closed when the throttle valve is closed. At this point, the ECM measures 0 volts and there is 0 volts at the IDL terminal. When the throttle is opened, the switch opens and the ECM reads +B voltage at the IDL circuit.
TPS in the ETCS-i System
Throttle Position Sensor
Throttle Position Sensor
The TPS on the ETCS-i system has two contact arms and to resistors in one housing. The first signal line is VTA1 and the second signal line is VTA2.
VTA2 works the same, but starts at a higher voltage output and the voltage change rate is different from VTA1 As the throttle opens the two voltage signals increase at a different rate. The ECM uses both signals to detect the change in throttle valve position. By having two sensors, ECM can compare the voltages and detect problems.
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