P0121 Decoded: Your 2023 GMC Yukon's Throttle Signal Issue
When your 2023 GMC Yukon throws a P0121, the ECM is telling you the throttle position sensor signal isn't tracking correctly. The voltage reads within specs, but the movement pattern is erratic—like watching a surveillance feed where the suspect's movements don't match the timeline. Something is disrupting the smooth correlation between your pedal input and throttle plate position.
The 2023 Yukon carries over GM's T1 platform with the 5.3L V8 (L84), 6.2L V8 (L87), or 3.0L Duramax diesel. All gas engines feature DFM and dual injection (port + direct), with the throttle body playing a central role in managing airflow across deactivation patterns.
Telltale Symptoms
- Check engine light on with Reduced Engine Power possible
- Stumble or delay when accelerating from idle
- Rough idle that smooths out at higher RPM
- Jerky transitions during highway cruising (DFM mode changes)
- Intermittent loss of throttle response
Investigation: Likely Causes
- Throttle body carbon contamination – Even at relatively low mileage, the throttle body can collect deposits that impede smooth plate travel. This remains the most common trigger. Likelihood: 45%
- Electronic throttle body failure – Internal motor or TPS sensor wear within the integrated assembly. Less common on a vehicle this new but not unheard of. Likelihood: 20%
- ECM software issue – GM has released multiple calibration updates for the T1 platform's throttle management and DFM integration. Likelihood: 20%
- Wiring or connector fault – Loose connector, corroded terminal, or chafed wire in the throttle body circuit. Likelihood: 10%
- Air induction leak – A loose clamp or cracked boot between the MAF sensor and throttle body. Likelihood: 5%
Repair Cost Breakdown
- Throttle body cleaning: $100–$180 (shop)
- Throttle body replacement: $350–$650 parts and labor
- ECM software update: $100–$200 (dealer only)
- Wiring repair: $100–$300
Take It to the Dealer
Your 2023 Yukon is solidly within GM's 3-year/36,000-mile bumper-to-bumper warranty and 5-year/60,000-mile powertrain warranty. This repair should be covered at no cost. The dealer will use GDS2 to analyze the throttle body data, perform a relearn, and apply any available software updates before considering hardware replacement.
How AutoDetective AI Can Help
Upload your scan data to AutoDetective and let our AI detective analyze the freeze frame data, engine variant, and mileage specific to your 2023 Yukon. Get a prioritized diagnosis and cost estimate before your dealer visit.