P0122 on GMC: How to Diagnose & Fix
Throttle/Pedal Position Sensor/Switch 'A' Circuit Low Input
1 GMC model · 1 documented issue · $250-$650 repair
P0122 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)
P0122 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 P0122 mean on a GMC?
P0122 stands for "Throttle/Pedal Position Sensor/Switch 'A' Circuit Low Input." This generic code means the PCM detected a lower-than-expected voltage from the throttle position sensor (or accelerator pedal position sensor) 'A' circuit. This sensor tells the computer how far the throttle/pedal is open so it can manage fuel, timing, and on drive-by-wire systems the throttle itself. A low or lost signal can cause hesitation, surging, poor acceleration, stalling, or limp-home mode, so it should be diagnosed promptly. On GMC it is documented across 1 model: Terrain.
What are the most common causes of P0122?
The most common causes of P0122 are: Faulty throttle position sensor, Short to ground or open in the TPS signal circuit, Damaged or corroded TPS connector, Loss of reference voltage or bad ground to the sensor, Worn throttle body / TPS contacts, Chafed or pinched wiring harness, Faulty PCM (rare). The specific cause varies by vehicle.
How much does it cost to fix P0122 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.