P2138 on GMC: How to Diagnose & Fix
Throttle/Pedal Position Sensor D/E Voltage Correlation
1 GMC model · 1 documented issue · $250-$650 repair
P2138 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)
P2138 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 P2138 mean on a GMC?
P2138 stands for "Throttle/Pedal Position Sensor D/E Voltage Correlation." This code means the two (or three) signals from the accelerator pedal position / throttle position sensors disagree with each other — specifically sensors 'D' and 'E', which are typically the redundant signals built into the electronic accelerator pedal. Drive-by-wire systems use multiple sensors that should track together so the computer can trust the driver's input; when their voltages don't correlate, the computer can't be sure of the requested throttle and sets this code. As a safety response it usually puts the engine into a reduced-power 'limp' mode. It generally points to the pedal sensor assembly or its wiring. On GMC it is documented across 1 model: Terrain.
What are the most common causes of P2138?
The most common causes of P2138 are: Faulty accelerator pedal position sensor assembly, Corroded or loose pedal sensor connector, Chafed, shorted, or open wiring between pedal and ECM, Shorted-together signal wires in the pedal harness, Poor sensor ground or reference voltage, Moisture or contamination in the pedal connector, Faulty ECM/PCM (less common). The specific cause varies by vehicle.
How much does it cost to fix P2138 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.