Parts for your 2009 Subaru Impreza-Throttle position sensors

2009 Subaru Impreza throttle position sensors — what they do and how to look after them

Based on technical sources — the Subaru Factory Service Manual for the 2009 Impreza (Engine Control/ETC section and DTC listings P0121–P0123), Subaru’s FAST electronic parts catalogue, and mainstream repair manuals for the GE/GH/GR-chassis — the 2009 Subaru Impreza absolutely uses throttle position sensing. It’s built into the electronic throttle body as part of the drive‑by‑wire system, and works alongside an accelerator pedal position sensor. On this model, the TPS is typically integral to the throttle body rather than a separate bolt‑on part.

The throttle position sensor’s job is straightforward but critical: it tells the engine control module exactly how far the throttle plate is open, moment to moment. Paired with the motorised throttle actuator and the pedal sensor, it lets the ECU manage airflow, fuel delivery, ignition timing and idle speed with fine control. That’s why when a TPS signal goes flaky, the Impreza can feel hesitant, hunt at idle, surge, or drop into limp mode, often flagging codes like P0121, P0122 or P0123.

As part of regular servicing, it’s smart to keep the throttle body clean and the electrical connections healthy. On these Imprezas, the sensor itself isn’t usually serviced on its own, technicians clean the throttle bore and plate with a throttle‑body safe cleaner (not a harsh carby spray) and check the harness and connector for corrosion or broken pins. Don’t force the throttle plate open by hand — that can upset the actuator gearing.

• If the battery’s been disconnected or the throttle body cleaned/replaced, an idle relearn or throttle “initialisation” may be needed. A short test drive with varied loads and a few minutes of idling usually lets the ECU relearn, or a scan tool can run the ETC relearn routine.
• Chasing a fault? Use a scan tool to watch “Throttle Position/Angle,” “Commanded Throttle,” and “Accelerator Pedal Position.” Mismatch, dropouts, or noisy signals point to wiring, connector, or throttle body issues.
• Replacement: because the TPS is integrated, many workshops fit a complete throttle body assembly when the sensor fails or is out of spec. Always use a new gasket, check for vacuum leaks, and complete the relearn.

Look after the system and the 2009 Impreza’s throttle control stays crisp, fuel use stays tidy, and drivability remains spot on.

Popular questions about 2009 Subaru Impreza throttle position sensors

Does the 2009 Subaru Impreza have a throttle position sensor?
Yes. The 2009 Impreza uses electronic throttle control, and the TPS is built into the throttle body. There’s also an accelerator pedal position sensor on the pedal. The factory manual and parts catalogue both show the TPS as part of the throttle body assembly rather than a separate external sensor.

What are the symptoms of a failing TPS on this model?
Common signs include erratic idle, hesitation on take‑off, surging at steady speed, poor fuel economy, and the car dropping into limp mode. The check engine light often comes on with codes like P0121–P0123. A scan tool will usually show jittery or mismatched throttle angle data when the TPS is misbehaving.

Do I replace just the sensor or the whole throttle body?
On most 2009 Imprezas, the TPS is integral to the throttle body, so workshops typically replace the entire throttle body assembly. Aftermarket standalone sensors exist in some markets, but fit and reliability can vary. If the body is replaced, complete a throttle/idle relearn and inspect the wiring and gasket to avoid repeat faults.