1. Function, classification, and identification of throttle position sensors
(1) Function
The throttle position sensor is one of the most important sensors in automotive electronic control systems, primarily used in engine electronic fuel injection systems and electronically controlled automatic transmission systems. Mounted on one end of the throttle body and throttle shaft, the throttle position sensor detects or monitors the size and rate of change of the throttle opening, converting the position signal into an electrical signal which is then input to the electronic control unit (ECU). This signal is used to determine various engine operating conditions, thereby controlling different fuel injection quantities and ignition timings. In vehicles equipped with electronically controlled automatic transmissions, the throttle position sensor signal is the primary signal for transmission shifting and torque converter lock-up.
(2) Types of throttle position sensors
Traditional cable-operated throttle valves are equipped with throttle position sensors, which are classified by their overall structure into contact switch type, sliding resistor type, and integrated type combining idle switch and sliding resistor. Newer intelligent electronic throttle valve control systems commonly use throttle position sensors of two types: dual sliding resistor type and linear dual Hall effect type.
Currently, the main types of throttle position sensors used in engine electronic control systems are Hall effect sensors and dual sliding resistor sensors. Toyota Camry and Corolla use Hall effect sensors; Nissan Teana and Buick Excelle use dual sliding resistor sensors.
2. Hall effect throttle position sensor
(1) Structural principle and installation location
The 2016 Toyota Camry Hybrid (engine model 6AR-FSE) uses a non-contact dual Hall effect throttle position sensor, the structure of which is shown in the figure below. It mainly consists of a Hall effect element and a magnet, with the magnet mounted on the throttle shaft and able to rotate around the Hall effect element.
The control circuit and signal output characteristics of the Hall effect throttle position sensor are shown in the figure above. When the throttle opening changes, the magnet rotates accordingly, thereby changing its relative position with the Hall element, which is surrounded by a magnetic yoke. The Hall effect integrated circuit converts the change in magnetic flux into an electrical signal and outputs it to the ECM in the form of a throttle position signal.
The throttle position sensor has two sensor circuits: VTA1 and VTA2, each emitting a signal. VTA1 is used to detect the throttle opening, and VTA2 is used to detect faults in VTA1. The sensor signal voltage is proportional to the throttle opening, varies between 0 and 5V, and is transmitted to the ECM terminals VTA1 and VTA2.
When the throttle is closed, the sensor output voltage decreases; when the throttle is open, the sensor output voltage increases. The ECM uses these signals to calculate the throttle opening and controls the throttle actuator to respond to driver input. These signals are also used to calculate air-fuel ratio correction, power boost correction, and fuel cut-off control.
(2) Circuit connection
The circuit diagram of the throttle position sensor for the 2016 Toyota Camry Hybrid is shown below.
The throttle position sensor is integrated into the throttle body assembly E16. E16 has six pins. Pins 1 and 2 are the throttle actuator motor control ports. Pins 6 and 4 output throttle position signals VTA1 and VTA2 to ports 122 and 88 of the engine control unit (ECU) E81(F), respectively. Pin 5 is the VCTA5V reference voltage provided by ECU 121; pin 3 is grounded via ECU 120.
(3) Detection
① Check the sensor power supply: Disconnect the throttle body connector E16 and use a multimeter to measure the voltage between E16/5 and E16/3. It should be 4.5 ~ 5.5V . Otherwise, check the ECU power circuit. If the ECU power circuit is normal, replace the ECU.
② Check the sensor signal voltage: Connect the diagnostic tool, turn on the ignition switch, press the accelerator pedal, and read the throttle position sensor data VTA1 and VTA2. The values should conform to the table below.
③ Check the sensor wiring harness and connectors: Disconnect the throttle body connector E16 and the engine control unit (ECM) connector E81. Check the resistance values between the connectors or between the connectors and the vehicle ground as shown in the table below. The resistance values should conform to the table. If they do not conform, replace or inspect the wiring harness.
3. Sliding resistive throttle position sensor
(1) Structure
The sliding resistance throttle position sensor, also known as the linear output throttle position sensor, variable resistance throttle position sensor, or potentiometer throttle position sensor, is currently widely used in automobiles, particularly the dual variable resistance throttle position sensor.
The sliding resistor-type throttle position sensor is a three-wire sensor. Two pins are located at the two ends of the resistor, serving as the power supply and ground terminals, respectively, and are supplied with 5V voltage by the engine ECU. The third pin is connected to the sliding contact. The throttle shaft and the contact (or contact head) are linked. When the throttle rotates, the sliding contact moves across the resistor, causing a change in the potential of the sliding contact. This change in resistance is used to convert the throttle position signal into a voltage value, as shown in the diagram. Because this voltage changes linearly, it is also called a linear output throttle position sensor. Based on this linear voltage value, the ECU can sense the throttle opening and make adjustments to the fuel injection quantity.
(2) Sensor detection
The throttle position sensor circuit for the 2013 Buick Excelle is shown in the diagram below. The engine control module provides a 5V reference voltage circuit to the throttle position sensor and a ground circuit to the low reference voltage circuit. The signal voltage provided by the throttle position sensor varies with the throttle opening. The throttle position sensor signal voltage is less than 0.5V at idle. The throttle position sensor voltage is generally close to 0V at idle, but may be as high as 0.5V . At full throttle (WOT), the throttle position sensor voltage should increase to above 4V.
The throttle position sensor detects the following:
① Turn off the ignition switch and disconnect the wiring harness connector on the throttle body assembly.
② Measure the resistance between the 5V reference terminal 2# and the low-voltage reference terminal 1# of the throttle position sensor. Check if the resistance is between 5.0 and 5.3 kΩ. If the resistance is not within the specified range, replace the throttle body assembly.
③ Measure the resistance between signal terminal #3 and low-pressure reference terminal #1 of the throttle body assembly. Test the throttle sensor across its entire range. The resistance should vary between 2.5 and 6.8 kΩ without any peaks or troughs. If the resistance is outside the specified range or unstable, replace the throttle body assembly.
④ Connect the throttle sensor to the applicable terminals using 5V and ground, and test the voltage between the signal terminal and the low-voltage reference terminal. Test the throttle sensor across the entire range. The voltage should fluctuate between 0.6 and 4.7V without any peaks or troughs. If the voltage is outside the specified range or unstable, replace the throttle body assembly.
(3) Dual variable resistance throttle position sensor
In a dual variable resistance throttle position sensor, the two sensors are typically installed together. This allows for timely identification of a fault in one sensor, increasing system reliability. Based on the relationship between the output signals of the two sensors, there are two types: inverse phase and in-phase. In-phase sensors can be further divided into linear changes with the same slope and linear changes with different slopes.
The structure and internal circuit of the BOSCH dual variable resistance throttle position sensor are shown in the figure below.
The dual-rail throttle position sensor on the throttle shaft monitors the accurate throttle opening. The sliders of the throttle position sensor (two potentiometers) are coaxial with the throttle body. When the throttle body rotates, the potentiometer sliders rotate synchronously. When a 5V operating voltage is applied, the changing resistance is converted into a voltage output signal. The potentiometer output voltage changes with the throttle position, allowing the control unit to accurately determine the throttle opening. Because the two potentiometers are installed in opposite phases, when the throttle position changes, both signal voltages change linearly; one increases while the other decreases. The following diagram shows the output characteristics of the throttle position sensor in Nissan vehicles.
The Nissan Teana series dual variable resistance sensor circuit is shown in the figure below.
The engine control unit (ECM) provides a 5V reference voltage to sensor terminal 1 via terminal 72; sensor terminal 4 is grounded via terminal 36 of the ECM. Throttle position signals TPS1 and TPS2, output from sensors 2 and 3 respectively, are sent to terminals 33 and 36 of the engine control system.
The inspection of the dual variable resistance throttle position sensor (taking Nissan Teana as an example) is as follows:
Turn on the ignition switch and shift the gear lever to D (A/T) or 1 (M/T). Use a multimeter in voltage mode to check the voltage between ECM ports 33 (signal from throttle position sensor #1) and 34 (signal from throttle position sensor #2) and ground under different accelerator pedal positions. The results should conform to the specifications in the table below. If they do not conform, replace the throttle body assembly.
4. Switch-type throttle position sensor
(1) Structural principle
The switch-contact type throttle position sensor is also known as a throttle switch. It has two sets of contacts: an idle contact (IDL) and a high-load contact (PSW). In the diagram below, a cam coaxial with the throttle body controls the movable contact (TL or E), causing it to open and close the two switch contacts according to the throttle body's state. When the throttle body is fully closed, the idle contact (IDL) is connected to the movable contact (TL or E). The ECU uses this idle signal to determine that the engine is in idle mode and controls engine operation accordingly. When the throttle body opens, the idle contact opens, and the ECU uses this signal to control engine operation from idle to low-load conditions. The high-load contact remains open from the fully closed position to a small to medium opening. When the throttle body opens to a certain angle, the high-load contact connects to the movable contact (TL or E), sending a signal to the ECU that the engine is operating at full load. The ECU uses this signal to perform full-load enrichment control.
