P0120 on GMC: How to Diagnose & Fix
Throttle/Pedal Position Sensor Circuit Malfunction
1 GMC model · 1 documented issue · $250-$650 repair
P0120 on GMC by model: symptoms, diagnosis and fix
First-generation Terrains (2010-2017) are prone to a sudden 'Reduced Engine Power' warning caused by a failing electronic throttle body. Carbon and grime build up inside the bore and the internal throttle position sensor (TPS) fails or reads erratically, causing the ECM to enter a limp/reduced-power mode that limits the vehicle to very low speed. This is a widely reported failure on the naturally aspirated 2.4L four-cylinder and 3.6L V6 engines and frequently appears alongside a 'Service StabiliTrak' message. The most commonly cited trouble code is P2135 (throttle/pedal position sensor voltage correlation). No NHTSA recall covers the throttle body; it is addressed through non-recall repair.
Common Symptoms
- 'Reduced Engine Power' message on dash
- Sudden loss of acceleration / limp mode
- Check engine light
- 'Service StabiliTrak' message
- Rough idle or stalling
How to Fix
Clean the throttle body if carbon buildup is the cause; if the throttle position sensor has failed the electronic throttle body assembly is replaced as a unit and the idle/throttle relearn procedure is performed.
Sources for this issue (2)
P0120 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0120 mean on a GMC?
P0120 stands for "Throttle/Pedal Position Sensor Circuit Malfunction." This code indicates a malfunction in the throttle position or accelerator pedal position sensor circuit. These sensors tell the computer how far the throttle plate is open or how far you've pressed the pedal, which the computer uses to control engine power and, on drive-by-wire systems, the throttle itself. When the signal is out of range, erratic, or doesn't make sense relative to other inputs, P0120 sets. Symptoms can include hesitation, surging, stalling, or the vehicle entering a reduced-power 'limp' mode for safety. On GMC it is documented across 1 model: Terrain.
What are the most common causes of P0120?
The most common causes of P0120 are: Failed throttle position sensor, Corroded or loose TPS/pedal sensor connector, Damaged or shorted sensor wiring, Carbon buildup or a sticking throttle body, Worn throttle body or throttle plate, Poor sensor reference voltage or ground, Faulty accelerator pedal position sensor, Faulty PCM/ECM (rare). The specific cause varies by vehicle.
How much does it cost to fix P0120 on a GMC?
Published repair estimates on GMC range from $250 to $650 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.