What Does P0121 Mean on a 2021 Chevrolet Tahoe?
Our diagnostic team has traced the P0121 clues on your 2021 Chevrolet Tahoe to the throttle position sensor (TPS). This code indicates the TPS is sending voltage within the expected range but with a pattern that doesn't match what the ECM calculates based on other engine parameters. The sensor is communicating, but its readings are inconsistent with the bigger picture.
The 2021 Tahoe is the first year of the all-new T1XX platform, a completely redesigned full-size SUV. Engine options include the 5.3L V8 (355 hp) with Dynamic Fuel Management, the 6.2L V8 (420 hp), and the 3.0L Duramax turbo-diesel (277 hp). The V8 engines use a combination of direct and port injection, while the diesel uses direct injection only. All rely on precise electronic throttle control.
Common Symptoms to Watch For
- Check engine light or Reduced Engine Power message
- Hesitation during acceleration
- Rough or fluctuating idle
- Sluggish throttle response when towing or hauling
- Dynamic Fuel Management (cylinder deactivation) may not operate smoothly
- Magnetic Ride Control may feel off due to drive mode confusion
Top Causes Ranked by Likelihood
- Carbon buildup on throttle body (35%) – Despite the dual-injection system on the V8s, some carbon accumulation occurs on the throttle bore from PCV gases. The 3.0L diesel is more susceptible as a DI-only engine. Cost: $150–$300.
- Throttle body assembly defect (25%) – As a first-year redesign, manufacturing variability is higher. An internal TPS defect can cause abnormal voltage patterns. Cost: $0 under warranty; $350–$600 otherwise.
- ECM software calibration (20%) – First-year T1XX models received numerous calibration updates. An outdated version may trigger false P0121 codes. Cost: $0 under warranty; $120–$200 otherwise.
- Wiring or connector issue (15%) – New platform wiring routes may have unforeseen chafe points or connector quality issues. Cost: $0 under warranty; $100–$300 otherwise.
- Intake system leak (5%) – A gasket or clamp issue in the intake tract. Cost: $0 under warranty; $100–$300 otherwise.
How Serious Is This Code?
P0121 is medium severity. The Tahoe's size and towing capability make reliable throttle response critical. The Reduced Engine Power mode on the T1XX platform can activate during critical moments. Address this soon.
Diagnostic Path
For a 2021 model, start at the dealer. They'll use GDS2 to read live TPS data, check for calibration updates, and search for TSBs applicable to your build date. The first-year T1XX had several software-related bulletins addressing driveability concerns.
If diagnosing yourself, monitor TPS voltage during slow throttle sweeps. Check for companion codes and review freeze frame data. On the diesel, inspect the throttle body for soot accumulation from EGR operation.
Can You Fix This Yourself?
Check warranty status—your 2021 Tahoe may still be within the 3yr/36k bumper-to-bumper warranty depending on purchase date and mileage. The 5yr/60k powertrain warranty likely still applies. Use the warranty first. If expired, throttle body cleaning is a moderate DIY job on the V8 engines, though access is tighter on the T1XX platform than the older K2XX.
Get a Free AI Diagnosis
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