Parts for your 2010 Subaru Legacy-Throttle position sensors

2010 Subaru Legacy throttle position sensor (TPS)

Referencing Subaru’s 2010 Legacy/Outback factory service manual (Engine Diagnostics for DTCs P0121–P0123, P2135) and guidance in the Subaru Technical Information System, the 2010 Subaru Legacy runs electronic throttle control. The throttle body houses dual throttle position sensors alongside the throttle actuator motor. On this model the TPS is integrated and non-serviceable, Subaru supplies the throttle body as a complete unit when TPS faults are confirmed. This design matches Denso’s OE electronic throttle body layout used by Subaru for these vehicles.

On a 2010 Legacy, the TPS tells the engine control module exactly where the throttle plate sits. That live angle data is critical for smooth tip-in, fuel and ignition timing, idle control, cruise control, and stability/traction strategies. With drive-by-wire there are typically two TPS tracks inside the throttle body that cross-check each other for safety. If the signals disagree, the car can drop into limp mode to protect the engine and driver.

Common TPS-related symptoms include a stubborn idle, hesitation off the line, hunting revs, poor fuel economy, cruise control cutting out, and the check engine light with codes like P0121, P0122, P0123 or P2135. Because the sensors are built into the throttle body, you don’t “adjust” a TPS on these—fault tracing is done with a scan tool, live data, and wiring checks. If the TPS is faulty, the fix is replacing the throttle body assembly and the gasket.

• Inspection tips: Check for intake leaks, clean the throttle bore with proper throttle-body cleaner (don’t drown the electronics), and confirm battery/charging health—low voltage upsets sensor readings.
• Replacement pointers: Use a quality gasket, torque the fasteners evenly, and don’t force the throttle plate by hand. After refit, perform an idle/throttle relearn. Many scan tools support ETC relearns, otherwise, follow the service manual drive/idle procedure.
• Service interval: There’s no set replacement interval for the TPS. As part of routine servicing, a light throttle-body clean every 40–60,000 km and a quick scan of TPS percentage and correlation values keeps things sweet.

Done right, a healthy TPS gives the 2010 Legacy crisp response and consistent economy. If faults persist after cleaning and checks, testing the harness for corrosion or broken grounds before fitting a new throttle body can save a few dollars.

Popular questions about 2010 Subaru Legacy throttle position sensors

Where is the TPS on a 2010 Subaru Legacy?
The TPS is built into the electronic throttle body on the intake manifold. It’s not a separate bolt-on sensor, the whole throttle body houses the dual TPS and the actuator motor.

Can the TPS be adjusted or replaced on its own?
No. On this model the TPS is non-adjustable and not supplied separately. Diagnosis focuses on live-data correlation and wiring integrity. If the sensor is faulty, the remedy is a complete throttle body replacement.

Do I need a relearn after replacing the throttle body or disconnecting the battery?
Yes. The ECU needs to relearn throttle and idle parameters. Use a scan tool’s throttle/idle relearn, or follow the factory procedure involving key-on cycles and a short drive. Skipping this can cause a shaky idle or delayed throttle response.