Throttle Position Sensor (TPS) off car
There are two types of TPS, either a potentiometer type or a switch type.
the first one I tested was a Potentiometer type:
-a potentiometer type has variable resistors which have a sliding contact
which moves with the throttle butterfly across the variable resistors changing
resistance.
-the one i tested had 3 wires; signal. earth and supply.
To test to see if the TPS i had was a potentiometer type I used a multimeter on the resistance scale, I connected the red probe to the supply wire and the black probe on the signal wire.
at this point the throttle butterfly was closed therefore on the multimeter the reading was low, this reading indicates the sliding contact is closest to the supply side and as you open the the throttle butterfly the resistance changes from a low reading to a higher reading, depending how much the butterfly opens.
Now i connected a power supply to the TPS using only 5 volts (didnt use a higher voltage because it could damage the sensor) to test the voltage output at different throttle angles, the angle the butterfly is at.
Throttle Angle (degrees) | Voltage output (V) |
0 | 0.714 |
22.5 | 1.15 |
45 | 1.96 |
67.5 | 2.76 |
90 | 3.86 |
At 0 degrees the output is low but still puts out a voltage which is a signal sent to the ECU, this signal tells the ECU that the throttle butterfly is fully closed which means its in the idle situation. When the throttle angle is at 45 degrees the voltage has increased due to the sliding contact on the variable resistors which means less resistance therefore a higher output voltage. This specific voltage lets the ECU know that the thottle is position is at its half point. At 90 degrees the throttle is at its wide open stage, the ECU knows this because this is the highest output the TPS sends out.
TPS switch type off car
4 pin- Idle, Half throttle, Full throttle and voltage in.
when the throttle is at idle the idle contact inside is connected to the voltage in pin, as the voltage passes through the idle circuit it encounters a resistance which changes the voltage output (the idle pin) this voltage is sent to the ECU to let it know that the throttle is at idle position, this is a low voltage. because this type doesnt have a half throttle pin it can't measure between idle and open throttle. As the throttle moves from idle to open throttle the resistance decreases because of this movement which therefore sends a voltage which is higher than the idle signal which tells the ECU that the throttle is at its wide open point.
TPS on-car/engine Potentiometer type
make: Toyota
Model: Corolla
Engine: 1zz
Reference voltage at the TPS
To locate the the 5v reference wire at the TPS on the 1zz i had to test each of the 4 wires with the ignition "on". By back probing the first wire with a pin (yellow wire) and by using a multimeter to measure the voltage input i got a reading of 4.86 volts which indicates that this is the 5v reference wire. This is a good reading because it is very close to 5v, the multimeter could have had some internal resistance in the multimeter itself. if the reading was below about 4.5 volts this would indicate that there is some resistance somewhere, possible reasons could be a loose connection with the plug and socket or wire split.
The purpose of testing the reference voltage to the TPS is to determine if it is getting the correct input voltage, if the input was incorrect e.g. low voltage the car will not run right because the ECU will be recieve incorrect signals.
Ground at TPS
To find which wire was the earth wire, like above, i back probed the black wire with a pin while the ignition was "on" and also measured the voltage at this wire. The reading i got was 0.4mV which is a good reading because it is in between 0.05v and 0.1v, depending on manufacturer.
This voltage at the earth of the TPS is important because it can tell you if the ECU has a good ground because the TPS is grounded through the ECU. If the reading were to be higher than 0.1v there could be a loose earth connection within the ECU or even from the ECU to the body of the vehicle. Also the earth wire could be split.
If the the grounding of the ECU was poor it would effect the operation of the engine and most of the sensors on it including the TPS. More voltage at the Earth would mean there is more resistance and therefore the input and output of the TPS would be wrong which would result in incorrect signals to the ECU.
TPS return/output/signal
With the engine off but with the ignition on and the throttle in the idle position i back probed the 3rd wire (white) also with a pin and measured the voltage output, I got a reading of 0.65v. Then i opened the throttle halfway and got a reading of 2.4v and then opened it to the full open position and got a reading of 4.85v. All these readings are as expected which means this TPS is in good working order.
As i opened the throttle slowly from the idle position to the fully open position and measured the voltage out put the reading gradually went up with no sudden gaps or jumps. This TPS also had a 4th brown wire which was an idle switch wire which should read 0v when closed and 12-14v when fully opened, I got these readings.
