P0639 indicates that the powertrain control module (PCM) has detected a performance problem in the throttle actuator control system for engine bank 2. The throttle plate did not move to the expected position within the specified time or range, causing the code to set. This can lead to reduced engine power, poor acceleration, and activation of a fail‑safe (limp‑home) strategy.
Carbon deposits or a stuck throttle plate can prevent the plate from moving smoothly, causing a mismatch between commanded and actual position.
The DC motor that drives the throttle plate may wear out or the gear may strip, reducing the ability to achieve the commanded position.
Open, short, or high‑resistance issues in the harness or connector for the bank‑2 throttle actuator can cause inaccurate control signals.
If the TPS provides incorrect voltage feedback, the PCM may think the throttle is not moving correctly.
A fault in the PCM’s throttle control circuitry or outdated calibration can trigger the code, but this is the least common cause.
Usually not; the fault lies in the throttle body, wiring, or sensors. PCM replacement is rarely needed and should be a last resort after confirming all other components.
Yes, carbon buildup that prevents the throttle plate from moving smoothly is one of the most common causes of P0639.
The vehicle will typically enter a reduced‑power mode (limp‑home) for safety. While you can drive a short distance, the condition should be diagnosed promptly to avoid stalling or poor performance.
Cleaning can resolve the problem if carbon buildup is the cause, but if the motor, gear, wiring, or sensor is faulty, cleaning alone will not fix the code.