What Does P0121 Mean on a 2024 Subaru Outback?
When P0121 appears on your 2024 Subaru Outback, our diagnostic detectives trace the evidence to the throttle position sensor (TPS). The sensor is transmitting voltage within the expected range but with a pattern the ECM considers abnormal—readings don't match calculations from pedal position, mass airflow, and engine load.
The 2024 Outback offers the 2.5L FB25 flat-four (182 hp) or the 2.4L FA24 turbocharged flat-four (260 hp in the Onyx Edition XT and above). Subaru's horizontally opposed (boxer) engines are unique in layout. The FB25 uses port injection, keeping the throttle body clean, while the FA24 turbo uses direct injection and is more carbon-susceptible. Both come standard with Subaru's Symmetrical AWD and a CVT (Lineartronic).
Common Symptoms to Watch For
- Check engine light on
- Hesitation during acceleration
- Rough or unstable idle
- CVT feels sluggish or hesitant
- EyeSight adaptive cruise may not respond smoothly
- Reduced throttle response in X-MODE
Top Causes Ranked by Likelihood
- ECM software calibration (35%) – Current-year vehicles benefit from ongoing calibration refinements. Cost: $0 under warranty.
- Throttle body manufacturing defect (30%) – Factory defect in the throttle body or TPS. Cost: $0 under warranty.
- Wiring or connector defect (20%) – Assembly variability. Cost: $0 under warranty.
- Carbon buildup on throttle body (10%) – Unlikely at low mileage; the FB25's port injection reduces risk further. The FA24 turbo is more susceptible. Cost: $130–$275 if not covered.
- Intake or boost leak (5%) – On the turbo, a boost leak; on the NA, an intake gasket issue. Cost: $0 under warranty.
How Serious Is This Code?
P0121 is medium severity. Your Outback is drivable but may feel underpowered. The CVT's reliance on accurate throttle data makes the issue more noticeable. Schedule a dealer visit soon.
Diagnostic Path
Take your 2024 Outback to a Subaru dealer. They'll use SSM (Subaru Select Monitor) to read live TPS data, check ECM software version, and search for applicable TSBs.
Can You Fix This Yourself?
Your 2024 Outback is covered by Subaru's 3yr/36k basic warranty and 5yr/60k powertrain warranty. Take it to the dealer—diagnosis and repair are free.
Get a Free AI Diagnosis
FB25 or FA24 turbo? AutoDetective's free AI diagnosis targets the most likely cause for your specific engine.