Throttle Position Sensor (TP)
SPECIAL NOTES: Note that the information provided in this guide is of a generic nature, and is intended for informational purposes only. However, since the basic operating principles of any given engine sensor is largely similar across all makes and models, it is possible to apply the information provided here to a large range of applications. Nonetheless, be aware that neither similarities in operation, appearance, or location, nor effects on engine operation when any given sensor fails is guaranteed, and it is therefore recommended that the relevant technical manual be consulted for details on the location, manufacturer specific diagnostic information, replacement procedures, and other technical information pertaining to the affected application. END OF SPECIAL NOTES.
What does the throttle position sensor do?
The Throttle Position Sensor (TPS) must not be confused with the Throttle Pedal Position Sensor (TPPS). The latter sensor is located on the accelerator pedal of applications that use drive-by-wire throttle control systems, while the former is used on applications that have a physical link such as a control cable between the accelerator pedal and the throttle body.
The throttle position sensor monitors the position of the throttle plate, which position is used by the PCM (Powertrain Control Module) to calculate appropriate fuel delivery strategies.
Why is a throttle position sensor needed?
The throttle position sensor provides the most direct input data to the PCM about the position, and rate of movement of the throttle plate, and this data is both compared and combined with input data from a variety of other engine sensors.
In practice though, the PCM needs additional data from other critical sensors as well. Therefore, only when the position of the throttle position sensor in combined with input data about the temperature of the intake air, the volume of air that enters the engine, the current engine speed/load, and the rate at which the position of the throttle plate is changing, is the PCM able to calculate an appropriate fuel delivery strategy. Put simply, the PCM is unable to calculate appropriate fuel delivery strategies without accurate, plausible, and reliable input data from a throttle position sensor.
How does a throttle position sensor work?
On most applications, the throttle position sensor is a simple potentiometer that is attached to the spindle of the throttle plate; as the throttle plate’s spindle rotates a moveable contact inside the sensor slides over a resistive element.
The resistive element forms part of a (typically) 5-volt reference voltage, which changes depending on where the sliding part contacts the resistive element. As a practical matter on most applications, if the throttle plate is in the closed position, the resistive element will have a high resistance (due to the position of the sliding part on the element), which means that a low voltage will be passed back to the PCM via a dedicated signal circuit.
As the throttle is opened, the sliding part moves across the element, which reduces the element’s resistance, which in turn, increases the signal voltage being passed back the PCM. The PCM interprets the changing signal voltage as degrees of rotation, which in a fully functional sensor, is directly proportional to the signal voltage.
It should be noted though that on almost all applications the PCM needs to learn the signal voltage that relates to the throttle plate being in the closed position in order to be able to compensate for wear in the sensor, and the throttle plate spindle bushings. Therefore, the prescribed relearning procedure must be performed whenever the throttle position sensor is replaced. However, on some applications, this procedure is performed automatically by the PCM during the first few drive cycles after a sensor replacement
Where is the throttle position sensor located on the engine?
The image above shows the location (arrowed) of the throttle position sensor on a typical throttle body. Note though that while the appearance of throttle position sensors vary somewhat between applications, it will always be located (on the throttle body) in such a manner that the throttle plate’s spindle can act directly on the sensor, without the need for actuators, linkages, or other intervening components.
What does the throttle position sensor look like?
The image above shows two sides of a typical throttle position sensor. While the image on the left shows the general appearance of the sensor, the image on the right shows some detail of the socket that engages with the spindle of the throttle plate.
Possible symptoms of a bad throttle position sensor
Throttle position sensors can fail in several ways; it can fail suddenly and unexpectedly, or it can fail gradually, with intermittent total failures being a relatively common feature of the latter failure mode. Regardless of how the sensor fails however, all failure modes have the potential to cause serious driveability issues, which obviously, have serious safety implications not only for the affected vehicle’s occupants, but for other road users as well.
Below are some common symptoms of a failed or failing throttle position sensor-
- Illuminated “CKECK ENGINE” light
- Poor fuel economy
- Idling may be rough, erratic, or the idling speed may fluctuate wildly- note that is some cases, the engine may not idle at all
- Engine may shut off or stall frequently and unexpectedly
- During driving at any speed, the engine power may unexpectedly increase or decrease in an unpredictable pattern
- The engine may not respond to throttle inputs
- On some applications, the PCM may initiate a fail-safe or limp mode as a safety precaution; note that in these cases, the PCM/TCM (Transmission Control Module) may lock the transmission into a particular gear, and prevent any gearshifts out of this gear until the problem is resolved
Note that depending on the application and the nature of the failure, one or more of the following generic codes may be present-
- P0120 – Throttle Pedal Position Sensor/Switch A Circuit Malfunction
- P0121 – Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem
- P0122 – Throttle/Pedal Position Sensor/Switch A Circuit Low Input
- P0123 – Throttle/Pedal Position Sensor/Switch A Circuit High Input
- P0124 – Throttle/Pedal Position Sensor/Switch A Circuit Intermittent
- P0220 – Throttle/Pedal Position Sensor/Switch B Circuit Malfunction
- P0221 – Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance Problem
- P0222 – Throttle/Pedal Position Sensor/Switch B Circuit Low Input
- P0223 – Throttle/Pedal Position Sensor/Switch B Circuit High Input
- P0224 – Throttle/Pedal Position Sensor/Switch B Circuit Intermittent
- P0225 – Throttle/Pedal Position Sensor/Switch C Circuit Malfunction
- P0226 – Throttle/Pedal Position Sensor/Switch C Circuit Range/Performance Problem
- P0227 – Throttle/Pedal Position Sensor/Switch C Circuit Low Input
- P0228 – Throttle/Pedal Position Sensor/Switch C Circuit High Input
- P0229 – Throttle/Pedal Position Sensor/Switch C Circuit Intermittent
In addition to the generic codes listed above, one or more of the following manufacturer specific codes may also be present, but note that some manufactures may use codes to indicate throttle position sensor issues that are not listed here-
- P1120 – Throttle position sensor out of range
- P1121 – Throttle Position (TP) Sensor Circuit Intermittent High Voltage
- P1122 – Throttle Position (TP) Sensor Circuit Intermittent Low Voltage
- P1123 – Throttle Position Sensor In Range But Higher Than Expected
- P1124 – Throttle Position Sensor Out Of Self Test Range
- P1125 – Throttle position sensor intermittent
- P1126 – Throttle Position (Narrow Range) Sensor Circuit Malfunction
- P1224 – Throttle Position Sensor B Out Of Self Test Range
- P1573 – Throttle Position Not Available
- P1574 – Throttle Position Sensor Disagreement Between Sensors
How to test the throttle position sensor
Testing a throttle position sensor is a relatively easy procedure, and should be well within the capabilities of most non-professional mechanics. Using a good quality digital multimeter and a repair manual (that applies to the affected application) that includes a wiring diagram, and proceed as follows-
Test the wiring
Locate the throttle position sensor on the throttle body, and disconnect the sensor’s electrical connector-
- Use the wiring diagram to determine the function and color-coding of each wire in the connector; there will generally be three wires- a ground, a signal wire, and a wire that carries the 5-volt reference voltage.
- Refer to the manual for details on the correct procedure to follow to test the reference voltage circuit for resistance and continuity. Note that fatal damage to the PCM can occur if the testing procedure is not followed exactly.
- Test the resistance and continuity of the signal and ground circuits in strict accordance with the instructions in the manual
If any tested electrical value does not agree with the specified values, repair or replace wiring as required to ensure that all electrical values fall within the specified ranges. If however, the wiring checks out OK, proceed as follows-
- Test the internal resistance of the sensor across the reference voltage and signal circuit terminals in the sensor’s connector. Be sure to identify these terminals correctly to avoid a misdiagnosis, and replace the sensor if the obtained reading does not match the specified value very closely.
- If the sensor’s resistance checks out OK reconnect the electrical connector, switch the ignition to the “ON” position, and verify that the correct reference voltage is present by back probing the reference voltage terminal in the connector and connecting the black lead of the multimeter to a suitable ground.
- If the reference voltage is present and correct, move the red probe to the signal wire, observe the displayed voltage, and compare this value to the specified voltage the sensor should pass when the throttle is in the closed position. Replace the sensor if this value deviates from the specified voltage by more than about two percent.
- If the closed position voltage is correct, slowly open the throttle manually and see if the signal voltage changes to the maximum allowable (and specified) voltage when the throttle in the fully open position.
- Note that the displayed voltage should change smoothly, and in direct response to any movement in the throttle plate’s position. If the displayed signal voltage does not change, changes in “steps” (i.e., does not change smoothly), or does not reach or exceeds the maximum specified value, the sensor is defective, and must be replaced.
How to replace the throttle position sensor
On most applications, the throttle position sensor is easily accessible on the throttle body, although is some cases, it may be necessary to remove cosmetic engine covers to gain easy access to the throttle body. One access is ensured, most throttle position sensors will follow the generic procedure outlined below-
- Disconnect the electrical connector
- Remove the retaining screws/bolts, and place them aside
- Remove the sensor from the throttle body, and insert the replacement
- Insert, and tighten all retaining screws/bolts, but do NOT over tighten to prevent damage to both the sensor and the throttle body
- Reconnect the electrical connector, clear all fault codes, and follow the instructions provided in the manual to perform the required relearning procedure if such a procedure is required
- Replace all cosmetic engine covers (where fitted) and test-drive the vehicle to verify the repair.