What Does P0121 Mean on a 2024 Nissan Altima?
When P0121 appears on your 2024 Nissan Altima, our diagnostic investigation reveals the throttle position sensor (TPS) is communicating within the expected voltage range but with an abnormal performance pattern. The ECM sees TPS data that doesn't align with its calculations from the accelerator pedal position sensor (APPS), mass airflow readings, and engine load.
The 2024 Altima is powered by Nissan's 2.5L QR25DE four-cylinder (188 hp) with a CVT. This engine uses multi-point injection (MPI)—also known as port injection—which has a significant advantage for throttle body health: fuel spray across the intake valves and ports helps wash away carbon deposits that direct-injection engines accumulate. The TPS is integrated into the electronic throttle body assembly.
Common Symptoms to Watch For
- Check engine light or MIL illuminated
- Hesitation during acceleration from stops
- Rough or surging idle
- Sluggish throttle response during highway passing
- CVT may feel hesitant or unresponsive
- Idle Stop feature may not function properly
Top Causes Ranked by Likelihood
- Throttle body manufacturing defect (35%) – On a brand-new vehicle, the most likely cause is a factory defect in the electronic throttle body or its internal TPS element. Cost: $0 under warranty.
- ECM software calibration (30%) – Nissan may have updated calibrations for the throttle body operation. Cost: $0 under warranty.
- Wiring or connector defect (20%) – Assembly-line variability in harness connections can cause intermittent TPS signal irregularities. Cost: $0 under warranty.
- Carbon buildup on throttle body (10%) – Unlikely at low mileage, and the MPI fuel system helps keep the throttle area cleaner than DI engines. Still possible with heavy short-trip use. Cost: $120–$250 if not warranty-covered.
- APPS or pedal assembly fault (5%) – A mismatched signal between the accelerator pedal and TPS can trigger P0121. Cost: $0 under warranty.
How Serious Is This Code?
P0121 is medium severity. Your Altima should remain drivable, but the hesitation paired with the CVT can make acceleration unpredictable. Schedule a dealer visit soon—this is fully covered under Nissan's warranty.
Diagnostic Path
Take your 2024 Altima to a Nissan dealer. They'll use CONSULT (Nissan's factory diagnostic tool) to read live TPS data, check for related codes, and verify ECM calibration version. The dealer has access to Nissan's TSB database for any known issues affecting your build date.
Can You Fix This Yourself?
Your 2024 Altima is under Nissan's 3yr/36k basic warranty and 5yr/60k powertrain warranty. Go to the dealer—diagnosis and repair are free. No reason for DIY on a vehicle with active warranty.
Get a Free AI Diagnosis
Want to understand the issue before your dealer appointment? AutoDetective's free AI diagnosis can analyze your 2024 Altima's symptoms and give you a detailed report to discuss with your service advisor.