Parts for your 2021 Subaru Impreza-Throttle position sensors

2021 Subaru Impreza throttle position sensors (TPS)

Based on Subaru technical information, the 2021 Subaru Impreza (FB20 2.0‑litre) does use throttle position sensors. The Subaru Factory Service Manual for the 2017–2021 Impreza (Engine/ECM and Fuel Injection sections, DTC P0121–P2135) and Subaru Electronic Throttle Control training materials specify an electronic throttle body that houses dual throttle position sensors, along with a separate accelerator pedal position sensor. The TPS units are integral to the throttle body and work as a matched set with the engine control module (ECM).

The TPS monitors the exact angle of the throttle plate so the ECM can meter fuel, spark and idle speed, and coordinate the CVT and cruise control. On these drive‑by‑wire cars, the ECM constantly cross‑checks the TPS against the accelerator pedal position to make sure what’s requested under the right foot is what the throttle is actually doing. If the signals don’t agree, it’ll flag a fault and may go into a reduced‑power “limp” mode to protect the engine and driveline.

On the 2021 Impreza the TPS isn’t a separate service item, it’s built into the throttle body. If the sensor fails or the correlation codes keep popping up, the fix is to replace the complete throttle body assembly and perform an idle/throttle learning procedure with a scan tool or brief drive cycle.

It’s not a part that needs routine replacement, but a bit of care helps. Every 60,000 km or so, check for carbon build‑up around the throttle plate. Lightly clean the bore with a throttle‑safe cleaner and a lint‑free cloth, battery off, and don’t force the plate open. Refit the intake plumbing snugly so there are no vacuum leaks under the bonnet.

Typical signs of TPS/throttle body issues include erratic idle, hesitation off the line, poor fuel economy, cruise dropping out, or a check engine light. Common codes are P0121–P0123 (TPS range/performance) and P2135 (correlation). If replacement is needed, use a new gasket, avoid contaminating the throttle motor or sensors, torque the fasteners correctly, and carry out the relearn so idle speed and tip‑in feel are spot on.

• Not serviceable separately: TPS is integral to the throttle body
• Keep the intake clean, don’t spray excessive solvent into the throttle
• After work, complete an ECM relearn or short mixed drive so it settles quickly

Popular questions about 2021 Subaru Impreza throttle position sensors

Does a 2021 Impreza actually have a TPS?
Yes. The 2021 Impreza uses an electronic throttle body with dual built‑in throttle position sensors, plus an accelerator pedal position sensor. The ECM compares these signals to manage airflow, fuel and idle, and to catch any mismatch for safety.

Can the TPS be replaced on its own?
No. On this model the TPS is integrated into the throttle body and isn’t serviceable as a separate part. If the sensor fails or correlation faults persist, the correct repair is to replace the complete throttle body and perform a throttle/idle relearn.

How do you reset or relearn the throttle after cleaning or battery disconnection?
Often the ECM will relearn on its own after a short mixed drive. A common method is to warm the engine, switch the ignition on for 10 seconds, then start and let it idle with no loads for a few minutes before a gentle drive. A proper scan tool relearn is ideal if idle hunts or the light returns.