What Does P0121 Mean on a 2024 GMC Acadia?
When your 2024 GMC Acadia logs a P0121, the ECM has detected that the throttle position sensor (TPS) signal falls within the expected voltage range but doesn't follow a logical pattern relative to the accelerator pedal position. Think of it as a detective noticing that a witness's story checks out on the surface but the details don't add up—something in the throttle body's signal is behaving erratically.
The 2024 Acadia rides on GM's redesigned platform with either a 2.5L turbo-four or an available 2.0L turbo-four, both featuring drive-by-wire electronic throttle control. The TPS is integrated directly into the throttle body assembly and communicates with the ECM through dual signal circuits for redundancy.
Common Symptoms You May Notice
- Reduced Engine Power message on the driver information center
- Rough or unstable idle, especially when cold
- Hesitation or stumbling during light acceleration
- Check engine light illuminated
- Slight surging at steady cruise speeds
Top Causes Ranked by Likelihood
- Carbon buildup on throttle body bore and plate – The turbo direct-injection engine is more susceptible to carbon deposits that restrict smooth plate movement. This is the #1 cause across GM's turbocharged lineup. Likelihood: 45%
- Throttle body assembly failure – Internal motor or sensor degradation within the electronic throttle body. Since the TPS is integrated, the entire unit needs replacement. Likelihood: 25%
- Wiring or connector issues – Corroded pins, chafed wiring, or loose connector at the throttle body harness. Road debris and moisture can accelerate this. Likelihood: 15%
- ECM software calibration – Outdated throttle body correlation tables. GM has released software updates for the new Acadia platform. Likelihood: 10%
- Intake air leak after throttle body – A cracked intake boot or loose clamp allows unmetered air, confusing TPS-to-airflow correlation. Likelihood: 5%
Estimated Repair Costs
- Throttle body cleaning: $80–$150 at a shop; $10–$20 DIY
- Throttle body replacement: $350–$600 parts and labor
- Wiring repair: $100–$250
- ECM software update: $100–$180 (dealer only)
DIY or Mechanic?
Your 2024 Acadia is covered under GM's 3-year/36,000-mile bumper-to-bumper warranty and 5-year/60,000-mile powertrain warranty. Take it to a GMC dealer first—this repair should be fully covered. After diagnosis, the dealer will use GDS2 to run throttle body relearn procedures and check for applicable Technical Service Bulletins specific to the new platform.
How AutoDetective AI Can Help
Upload your OBD-II scan data to AutoDetective's AI diagnostic tool and get a ranked list of likely causes specific to your 2024 Acadia's engine and mileage. Our system cross-references GM TSBs and known issues to pinpoint the most probable fix before you visit the shop.