P2138: How to Diagnose & Fix — Throttle/Pedal Position Sensor D/E Voltage Correlation

The 2007-2013 Avalanche frequently enters "Reduced Engine Power" mode, severely limiting acceleration. The most common causes are the electronic throttle body wearing out or the accelerator pedal position sensor (APP sensor) developing faults. The vehicle becomes barely drivable in this mode, struggling to accelerate to highway speeds. The issue can occur intermittently before becoming permanent.

The electronic-throttle-control warning lamp and reduced-power or limp mode are protective responses, not a diagnosis that the throttle body has failed. Depending on the stored DTC and application, the factory path may lead to a stuck or contaminated throttle plate, throttle motor or position-sensor response, accelerator-pedal sensors, a five-volt supply fault, damaged wiring or terminals, or a PCM issue. The old card's thermostat shopping claim is not part of the cited ETC diagnostic path, and a throttle body should not be ordered from the warning lamp alone.

The CD3 Edge uses a Ford electronic throttle body (ETB) with an integrated throttle position sensor. Non-conductive deposits build up on the internal sensor contacts, so the PCM sees an implausible or drifting throttle plate position and drops the vehicle into failsafe/limp mode - the amber wrench warning lights up and engine output is cut to idle-ish power, often at highway speed with no warning. Owners describe it as the truck 'just quitting on me' merging or passing, sometimes clearing after a key cycle and then recurring more frequently. Cleaning the throttle bore does not fix it because the fault is on the electronic contacts inside the sealed unit, not carbon on the plate. Ford extended ETB coverage on other models (program 13N03, certain 2.5L and 3.0L vehicles) but not the Edge, whose 3.5L/3.7L ETB failures were the subject of class-action lawsuits, and the failure is heavily represented in NHTSA complaints for the Edge.

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.

A widely reported Silverado 1500 complaint is a sudden cascade of dash messages — 'StabiliTrak disabled,' then 'Service StabiliTrak,' 'Service Traction Control,' and finally 'Engine Power Reduced' — sometimes with a stumble or stall and limited throttle response. The most common root causes are a faulty accelerator pedal position (APP) sensor or throttle body (electronic throttle), but GM bulletin 18-NA-161 also traces 'Service StabiliTrak' with engine stalling to high-resistance or loose battery cables, a poor BCM ground at G218 (behind the driver-side dash), a starter B+ cable shorting against the starter shield, or a weak battery. Because it can drop the truck into reduced-power limp mode at speed, owners treat it as urgent.