throttle position sensor / on car

Throttle Position Sensor (Potentiometer Type)

There are 2 types of tps sensors which is the switch type and the potentiometer type, just by looking at the shape of this type of tps sensor we can tell its a potentiometer type as its has a round shape.Switch types generally have a square shape.

The tps is mounted on the throttle body connected to the butterfly of the throttle. As the throttle opens and closes the voltage changes which is sent to the ecu. The ecu uses this voltage to know where the throttle is at example if its at idle or full throttle to do calculations to have good performance of the engine.

Firstly to determine what terminals were which on our tps we did a resistnce check with our multimeter on ohms and looked at our circuit diagram to see what kind of resistance we would get when we open and  closed  throttle.There was no change from vc and e2 so we knew that   that was the power and ground.  Resistance decreased from vc and vta  as we open the throttle. Resistance increased for e2 and vta as we opened the throttle. By all this information we found out what terminals were what on our tps. 

Internal operation

Reference voltage to the tps is supplied by the ecu and the output signal voltage is changed by a internal variable resistor regarding the position of the throttle. Generally When the throttle is opened resistance steady decreases the the voltage at signal steady increases and reaches maximum reference voltage at wide open throttle.

Vc gets generally a 5v suppy form the ecu. There is a variable resistor at vc and a wiper arm is connected to vta (signal). As the throttle opens and closes the wiper arms moves up and down across the variable resistor. Vta is in parallel with vc and the voltage at vta goes back to the ecu. The magnitude of the voltage at vta is dependent on at which place the wiper arm touches the resistor. As the throttle opens the wiper arms gets more closer to vc so the resistance decreases between vc and vta and the voltage is higher at vta. The resistance increases between  vcc and vta when the throttle is closed therefore less voltage is at signal (vta). This is how the ecu determines the position of the throttle. As the throttle opens voltage increases at signal.

Throttle angle	Voltage Output
0	0.61
15	1.22
30	1.93
45	2.21
60	3.12
75	3.8
90	4.18

On Car Reference Voltage at TPS

We back probed the reference wire on the TPs and connected the red lead of our multimeter reading DC volts. The black lead was connected to the ground. We got a reading of 4.97V.


The purpose of the reference voltage is to give the TPS a reference from where the variable resistor will pick up voltage regarding the position of the throttle. A incorrect reference voltage will give out incorrect signal voltage out to the ecu. Thing that cause this are:
 - Bad regulator in the ecu that regulates the voltage.
 - Open circuit between the 5v supply and the TPS.
 - Frayed wires  causing a high resistance to supply full voltage from the ecu.
 - corrosion on connections.

Ground At TPS

To check the ground on the sensor we back probed the sensor ground and connected the multimeter red to the TPS ground and the black lead to the battery negative. We started the engine. We got 0.0mV reading.


This showed us that there is a very good grounding present as there is hardly any voltage drop from the TPS earth and the battery. Its important to check this to diagnose problems and to see if there is any resistance on the earth side causing a voltage drop. A bad connection form the battery terminal to the battery post can cause a bad earth. Bad connection from the ecu ground to chassis. Also from the TPS sensor ground to chassis being loose or corroded. resistance in the ground side will cause incorrect voltages at signal.

TPS Return / Output

To see the output of the tps we back probed the tps signal and connected a multimeter to read Dc volts. Red lead to the signal and the black lead to battery negative. With the ignition on we got a reading of 0.618V. As i opened the throttle the voltage incresed. To about half throttle i 2.676V. As i open the throttle more the voltage gradually increased. When i readed Wide open throttle the voltage was 3.93V.


When i oped the throttle from closed to open throttle there was no sudden voltage jumps or gaps in the signal. The voltage increased as i opened it. Our TPS was a 3pin.


The tps is connected to the throttle body with a wiper arm connected to the throttle butterfly.As the throttle opens and closes the wiper arms moves across the variable resistor on the reference voltage. The magnitude of the voltage at the signal is dependent on where the wiper arm touches the variable resistor. The ecu sends a DC 5V to the variable resistor to ground. As the throttle is opened the wiper arm moves more close to the supply side therefore less resistance is present and more voltage is at signal. When the throttle closes the wiper arm moves more close to the earth side, therefore more resistance is present making less voltage at signal.


If there is no reference voltage the signal would read 0. If the reference voltage has shorted to signal, signal would always read reference voltage.If the tps ground has an open circuit and wont let the reference voltage get to ground, signal would reference voltage all the time.If there is a high resistance at the earth, the signal will be higher than normal even at closed throttle.


The wiring diagram is above in the Off car part.