P2135 on Chevrolet: How to Diagnose & Fix

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.

A 'Reduced Engine Power' warning that drops the car into limp mode (capped RPM and speed) is a common Camaro complaint traced to the electronic throttle body. When the two internal throttle-position sensors disagree, the PCM sets P2135 and limits power as a safety measure. It can also present as rough/shaky idle, stalling at stops, and hesitation on tip-in. Cleaning does not fix a sensor fault; the internal TPS has failed.

The electronic (drive-by-wire) throttle system triggers a 'Reduced Engine Power' / 'Engine Power Is Reduced' limp mode that sharply limits acceleration and speed - dangerous when it strikes in traffic. The cause is usually the throttle actuator control (TAC): worn internal throttle-body sensors/motor, or a broken/chafed wire in the harness a few inches from the throttle-body connector. Correlation codes P2135 and TAC-performance code P1516 are typical.

The GMT360 TrailBlazer uses a drive-by-wire throttle actuator control system with dual redundant sensors in both the throttle body and the accelerator pedal. When the two throttle position signals disagree the PCM sets P2135 and drops the truck into Reduced Engine Power limp mode — the vehicle will barely accelerate, which is dangerous when it happens pulling into traffic. Usual root causes are an internally failed electronic throttle body, a corroded or loose crimp in the throttle body connector, or moisture intrusion in the harness. Related codes P0641 (5V reference) and P1523 (throttle closed position performance) show up alongside it.

Tahoes with drive-by-wire throttle (APP pedal sensor + TAC module + electronic throttle body) commonly trigger a 'Reduced Engine Power' message and drop into limp mode with severely limited acceleration - a safety concern in traffic. On GMT800s the frequent culprits are a broken/chafed wire in the throttle-body harness (often the yellow wire), corroded engine grounds, or a dirty/sticking throttle body (P1516/P1515). GMT900s see similar throttle-actuator/APP faults (P2101/P2135/P0120 family).

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 it is also frequently traced to poor/corroded ground connections and chafed wiring under the driver's door sill or at the underseat/main harness connector. Because it can drop the truck into reduced-power limp mode at speed, owners treat it as urgent.

Impalas frequently throw a cluster of warnings at once — 'Engine Power Reduced,' 'Service StabiliTrak,' and 'Service Traction Control' — that are usually one underlying drive-by-wire fault rather than three separate failures. The most common root cause is the electronic throttle body actuator (or the dual throttle-position sensors inside it) going out of range; the accelerator pedal position sensors can also disagree. Because the ECM cross-checks these dual sensors, any disagreement forces the car into limp-home mode with drastically reduced power. Carbon buildup on the throttle plate aggravates it, especially in cold weather.

The Cobalt is drive-by-wire: the pedal module houses two redundant APP sensors, and the PCM compares them against the electronic throttle body's two TPS signals. When one signal drifts out of correlation the PCM drops the car into Reduced Engine Power mode — throttle authority is cut to a fast idle with the wrench/RE POWER message on the cluster, often with no warning in traffic. Owners report it as an intermittent that starts as a stumble and progresses to repeated limp events. P2138 (APP sensor 1-2 correlation) is the dominant code. The real cause is split between a worn pedal module, a dirty or failing electronic throttle body, and — very commonly on this car — corroded or loose connector terminals, since water intrusion down the A-pillar from a clogged sunroof drain reaches wiring in this area.