What does it mean?
OBD II fault code P0601 is defined as “Internal Control Module Memory Check Sum Error”, and is set when the PCM (Powertrain Control Module) detects either a breakdown in communication between itself and one or more supporting control modules, or between two or more supporting control modules. In all cases, the PCM acts as the central or main controller. When a breakdown in communication occurs in any area of the CAN system, a code will be stored and a warning light will be triggered.
However, depending on the application, several drive cycles (up to 8 in some cases) may be required to before a code is stored and a warning light is triggered. The CAN (Controller Area Network) typically includes control modules for systems such as, turbo boost control, ABS brakes, the instrument panel, anti-theft/security system, cruise control, fuel management, transmission control, climate control, proximity control, body control, and safety systems such as traction and stability control.
Note that this list is not exhaustive, and that the actual number of control modules that make up the CAN system is make and model specific. In practice, the CAN system monitors and controls every aspect of a vehicle’s operation by means of a system that allows all the microprocessors and controllers in a vehicle to constantly exchange messages and signals between themselves, and the sensors/systems they control.
This is accomplished by the complex interconnection of all affected wiring harnesses to create a “distribution pipeline” to carry input and signal voltages from, and to various sensors, components, systems, other controllers, and ultimately to and from the PCM. To illustrate how the system works (albeit in a grossly over simplified manner), imagine that the PCM receives a signal from the vehicle speed sensor.
Provided that the signal is valid and that the CAN system is in good working order, the PCM will make the signal available to the- cruise control system (if fitted) for speed control purposes, ABS brakes system, which will compare the signal and the actual vehicle speed to information collected from the wheel speed sensors to arm the brake, stability and traction control systems, fuel management system via the throttle position sensor (and others) for the purposes of calculating an appropriate fuel delivery strategy, transmission control system to regulate efficient shifting, and the proximity warning system, among others.
NOTE: The above example of CAN bus operation is not definitive, and is meant for general informational purposes only. It should therefore NOT be used in any diagnostic procedure relating to the CAN bus system. The image below shows a simplified approximation of which systems on a modern vehicle are interconnected by the Controller Area Network. Note that only critical systems are shown in this image. Other, non-critical like audio, GPS, lighting, security/anti-theft, and others are not shown.