U0641 means the engine/powertrain control module has lost data communication with the evaporative-emissions (EVAP) system pressure sensor or pressure switch circuit. It is a network/communication fault rather than a direct emissions-performance fault, so the problem usually lies in the wiring, connector, power supply, or the sensor/module itself. The exact component and circuit location depend on the vehicle make and model.
Open, short-to-power, short-to-ground, corrosion, terminal push-out, or harness damage in the power, ground, or data lines to the EVAP pressure sensor/switch is the most common cause of a lost-communication code.
The sensor, pressure switch, or leak-detection/EVAP module itself can fail internally and stop communicating on the data bus even if power and ground are present.
A blown fuse, bad relay, poor ground, or low/ref voltage feed can keep the EVAP sensor/module from waking up and responding to the PCM.
Intermittent or open CAN/LIN bus lines, poor termination, or interference between the EVAP module and the PCM can interrupt messages and set U0641.
A failed PCM is uncommon for this code; consider reprogramming or replacing it only after wiring, power, ground, the sensor/module, and bus integrity have been verified.
Yes, in most cases drivability is unaffected. However, the EVAP monitor may not run and the vehicle may fail an emissions test, so it should be diagnosed and repaired.
Not always. Lost-communication codes are often caused by wiring, connector, power, or ground problems. The sensor itself should be tested before being replaced.
Usually no. PCM failure is rare for this code. It should only be considered after verifying the wiring, power supply, ground, sensor/module, and data-bus integrity, and only if a reflash or module fault is confirmed.
If the underlying cause was a harness, connector, power, ground, or bus fault, replacing the sensor will not restore communication. The circuit must be fully tested and repaired.