P2109 – Accelerator pedal position (APP) / Throttle position (TP) sensor A – minimum stop performance

By Reinier (Contact Me)
Last Updated 2018-01-15
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P2109 Mean?
2. Where is the P2109 sensor located?
3. What are the common causes of code P2109?
4. Get Help with P2109

What Does Code P2109 Mean?

OBD II fault code P2109 is a generic code that is defined as “Accelerator pedal position (APP) / Throttle position (TP) sensor A – minimum stop performance”, and is set when the PCM (Powertrain Control Module) detects a malfunction of, or a failure in, the Accelerator Pedal Position (APP) / Throttle Position (TP) sensor labelled “A”.

Note that-

• This code refers to issues that influence how the engine runs when the accelerator pedal is not depressed. For instance, when there is no pressure on the accelerator pedal in a fully functional system, the pedal is said to be in the “minimum stop”, or closed position, and in this position, the engine must idle at, or close to the preset idling speed for that application
• This code only applies to applications that have “drive-by-wire” throttle control systems in which there is no physical link between the throttle plate and the accelerator pedal
• While this code refers to a particular Accelerator Pedal Position (APP) / Throttle Position (TP) sensor, not all manufacturers label sensors, circuits, and systems in the same order. For this reason, it is important to refer to repair manual for the affected application to determine which of several sensors in the throttle control system is labelled “sensor A” on that application

Modern “drive-by-wire” throttle control systems typically use two (or sometimes) more variable resistance sensors to control the position of the throttle plate relative to the position of the accelerator pedal. In practice, the accelerator pedal position sensor is supplied with a 5-volt reference voltage, and because the pedal acts directly on the sensor when the pedal is depressed or released, the resistance in the sensor changes in direct proportion to the pedal’s movement, thus allowing more or less current to be passed back to the PCM via a dedicated signal circuit.

The PCM interprets the changing signal voltage as a throttle/pedal position, and it uses this input data to calculate a degree of rotation of the throttle plate that corresponds to the position of the accelerator pedal. In practical terms, this means that as the accelerator pedal is depressed or released, the changing signal voltage is used by the PCM to open or close the throttle plate by means of a stepper motor that is connected to the throttle plate. In this way (provided there are no malfunctions in the system), the PCM provides throttle control that is as effective as if there had been a physical link such as throttle control cable between the accelerator and the throttle plate.

However, since accelerator pedal position sensors and the links that attach them to the actual pedal can wear out over time, it can happen that the PCM receives incorrect or invalid data when the accelerator pedal is in the minimum stop position. When this happens, the PCM can receive a signal voltage that is either above or below the expected or desired  voltage range, which can result in the idling speed falling outside of the expected/desired range on the one hand, or that the PCM can no longer control the throttle effectively during normal driving conditions, on the other.

On most applications when the PCM cannot control the throttle effectively, the PCM will set code P2109, illuminate a warning light, and initiate a failsafe, or limp mode, which it will maintain until the fault is corrected.

Where is the P2109 sensor located?

The image above shows an accelerator pedal in which the position sensor is incorporated into the pedal assembly. In this example, the part colored orange slides across a resistive element as the pedal is depressed or released, thereby creating the variable signal voltage. Note though that while almost all accelerator pedal position sensors work on this basic principle, the actual appearance and design of the position sensor varies greatly between manufacturers.

What are the common causes of code P2109?

NOTE: It should be noted that code P2109 is seldom seen in isolation. In most instances of this code, other codes relating the throttle actuator motor, throttle body, or correlation (failure to correlate) between two or more throttle control sensors are also present. Since many of these codes can cause P2109, or contribute to the setting of P2109, all additional codes must be resolved in the order in which they were stored before a diagnosis of P2109 is attempted. Failure to do this will result in a misdiagnosis, and the unnecessary replacement of parts and components.

Nonetheless, some common causes of code P2109 could include the following-

• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors almost anywhere in the throttle control system
• Defective Accelerator Pedal Position (APP) / Throttle Position (TP) sensor “A”
• Defective, broken, or worn mechanical linkage between the accelerator pedal and the Accelerator Pedal Position (APP) / Throttle Position (TP) sensor “A”
• Failed or failing PCM. Note that this is a rare event, and the fault must therefore be sought elsewhere before any control module is replaced

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