There are a whole series of components in a vehicle which allow acceleration to take place. The accelerator pedal assembly has a pedal position sensor and the intake manifold has a throttle position sensor on its throttle body. Whenever you step on the gas pedal to accelerate the vehicle, you are basically demanding more power from the engine. The harder you step on the pedal, the more urgent that power is needed.
The pedal position sensor and throttle position sensor detect how hard you press down on the gas pedal. The sensors send this information to the powertrain control module, which is the central computer of the vehicle. Based on the information provided, the computer will send more air and fuel into the internal combustion chamber of the engine so that it can generate more power. All of these things happen instantaneously after you step on the gas pedal.
The throttle position sensor starts out in a resting position but then rotates faster as acceleration is detected. During its rotation, the powertrain control module receives a voltage signal from the throttle position sensor. When the voltage signal is stronger, the powertrain control module increases the air to fuel ratio and timing of the ignition in the combustion chamber. When the voltage signal is weak, the powertrain control module decreases the air to fuel ratio and the timing of the ignition.
If the powertrain control module receives unusual data from the Throttle Position Sensor “A” Circuit, then it’ll trigger trouble code P0121. The symptoms associated with trouble code P0121 include knocking, jerking, poor acceleration, stalling, and the Check Engine light turning on. The common causes of the P0121 include bad throttle body, dirty throttle body, bad throttle position sensor, bad TPS connection, shorted TPS circuit, electrical terminal corrosion.
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These are all very serious problems which require immediate assistance. In most cases, your powertrain control module will activate a failsafe mode in order to reduce your acceleration speed limit. Once this happens, you should drive your vehicle to the mechanic right away to get the problem fixed. If you continue to let the problem persist without getting it fixed, then your engine could suffer irreparable damage.