Parts for your 2009 Subaru Legacy-Throttle position sensors

2009 Subaru Legacy Throttle Position Sensor (TPS)

Based on the Subaru Factory Service Manual for the 2009 Legacy/Outback (engine management and throttle control sections), Subaru Technical Information System wiring diagrams, and OBD-II diagnostic references, the 2009 Subaru Legacy does use a throttle position sensor. It’s built into the electronic throttle body assembly and works alongside the accelerator pedal position sensor as part of the drive-by-wire system.

The throttle position sensor on a 2009 Subaru Legacy lives inside the electronic throttle body, tracking the angle of the throttle plate and feeding precise position data back to the engine control module. That feedback is critical for smooth idle, crisp throttle response, correct fuelling, and effective emissions control. Because it’s part of the drive-by-wire setup, the TPS often comes as an integrated unit with the throttle actuator motor—so there’s no traditional cable and, on most models, no separate bolt-on TPS to replace by itself.

As part of routine servicing, it pays to keep the throttle body clean. Light carbon around the plate can skew TPS readings and cause odd idle behaviour or tip-in hesitation. A careful clean with throttle body cleaner (avoiding harsh scrubbing of the plate and shaft) can restore stable readings. After cleaning or battery disconnection, a throttle/idle relearn may be required—this can happen automatically after a short drive cycle, or can be commanded with a scan tool. If the car logs codes like P0121–P0123 or goes into limp mode with throttle control faults, diagnostics should confirm sensor correlation and wiring integrity before parts are swapped.

When replacement is necessary, most 2009 Legacy variants require replacement of the complete throttle body assembly. Fit a new gasket, don’t force the throttle plate by hand, and torque fasteners evenly. After install, clear codes, perform a relearn, and verify live data for pedal vs. throttle angle tracking. Regular checks during scheduled servicing—looking for stored fault codes, inspecting connectors for moisture or fretting, and confirming smooth throttle response—will keep the TPS and throttle control system happy for many more kilometres.

• Tell-tale signs: erratic idle, flat spots, sudden loss of power, poor fuel economy, or TPS/ETC fault codes.
• Best practices: clean the throttle body periodically, protect connectors with proper sealing, and use a scan tool to confirm sensor agreement.

FAQs: 2009 Subaru Legacy Throttle Position Sensor

Does the 2009 Subaru Legacy have a TPS or just a pedal sensor?
It has both. The accelerator pedal uses a pedal position sensor, and the throttle body contains a built-in throttle position sensor. The ECU cross-checks them for accuracy as part of the electronic throttle control system.

What symptoms point to a failing TPS on a 2009 Legacy?
Common signs include inconsistent idle, hesitation when taking off, sudden throttle drop-outs, and the car entering limp mode. The ECU may log codes such as P0121–P0123 or related throttle actuator correlation faults. Always confirm with live data and wiring checks.

Can the TPS be replaced separately, or does the whole throttle body need changing?
On most 2009 Legacy models the TPS is integrated into the throttle body, so replacement usually means fitting a complete throttle body assembly. Some aftermarket options claim separate sensors, but proper operation and calibration can be hit-and-miss. After any replacement, a throttle relearn is recommended.