If your vehicle is showing vehicle stuck in limp mode and won't go past a certain speed, here are the most likely causes and the parts you'll need to fix each one.
The engine computer relies on sensors like the Mass Air Flow or Throttle Position sensor to calculate fuel and air. If these fail or are left unplugged after an air filter change, the car enters limp mode to prevent runaway acceleration or engine damage.
Low transmission fluid, a clogged filter, or a failing shift solenoid will cause the transmission computer to lock the vehicle in a single gear (limp mode) to prevent internal clutch damage.
The VVT system adjusts engine timing using oil pressure. Dirty oil, the wrong oil viscosity used during a recent oil change, or a failed VVT solenoid can cause timing errors that trigger limp mode.
On turbocharged vehicles, a loose intercooler pipe or a faulty boost pressure sensor can cause an underboost or overboost condition, immediately forcing the car into limp mode to protect the engine.
A melted or clogged catalytic converter creates massive exhaust backpressure. The engine physically cannot breathe enough to exceed a certain RPM or speed, mimicking or triggering limp mode.
In rare cases, the computer itself (ECM or TCM) suffers an internal hardware failure, defaulting to limp mode because it can no longer process sensor data correctly.