U0401

U0401 is a diagnostic trouble code (DTC) that stands for "Internal Control Module CPU Malfunction." This code indicates that the powertrain control module (PCM) or engine control module (ECM), the vehicle's main computer responsible for engine operation, has detected an internal problem with its central processing unit (CPU). This malfunction can lead to a variety of drivability issues.

When this code is triggered, it means the PCM/ECM itself is not functioning correctly. This could be due to a hardware failure, a software glitch, or an electrical issue affecting the module's internal processing. Symptoms may vary widely and can include the check engine light illuminating, rough idling, stalling, poor acceleration, or even a complete failure of the engine to start. In some cases, the vehicle may enter a "limp mode" to prevent further damage, significantly restricting engine power.

Diagnosing a U0401 code typically involves scanning the vehicle for other related DTCs, checking the integrity of the PCM/ECM's electrical connections, and testing the module itself. If the PCM/ECM is found to be faulty, it will usually require replacement and reprogramming by a qualified technician. Due to the critical nature of the PCM/ECM, a U0401 code should be addressed promptly to ensure the vehicle's safe and reliable operation.