What does it mean?
OBD II fault code P0657 is most commonly defined as “Actuator Supply Voltage “A” Circuit/Open” and is set when either the PCM (Powertrain Control Module) or any other control module detects a break in communication between two or more control modules. Circuit “A” refers to a part of the CAN (Controller Area Network) circuit, rather than a specific circuit, wire, or component.
Note that the term “Circuit A” is not always included in the various definitions of this code, but where it is included, “Circuit “A” could mean different things on different applications. Always consult the manual for the application being worked on for detailed information on the exact meaning and correct interpretation of the definition.
SPECIAL NOTES: The Controller Area Network on any vehicle is a highly complex conglomeration of wiring harnesses, sensors, and other components that link most control modules to each other on the one hand, and all of the control modules to PCM on the other.
The system can be thought of as a sort of miniature intranet, where all of the control modules are in constant communication with each other, and where the PCM acts as a sort of “clearing house” or “sorting station” for the several thousand signals, pulses, and messages being passed every second between the various control modules that control every aspect of a vehicle’s operation. Regardless of the exact meaning of a definition assigned to code P0657, no control module can function in isolation.
All control modules are inter-connected via the CAN bus system, which in practice means that a loss of communication between a particular control module and the components/systems it controls directly affects other control modules and/or systems. Note though that while it is sometimes possible to repair the loss of communication between some controllers without dissecting the entire CAN bus system, this is not always possible. END OF SPECIAL NOTES.
The actual number of control modules varies between applications, with some applications having as many as 18, or sometimes more.
Typical control modules that are linked by the CAN system include the following, but are not necessarily limited to the- alternative fuel control module body control module antilock brake control module instrument panel control module fuel injection control module boost pressure control module anti-theft/security/alarm module cruise control module traction control module stability control module proximity alert module climate control module In practice, a signal from a particular sensor is often shared between multiple controllers.
For instance, a signal from the vehicle speed sensor is sent to the- PCM to manage engine functions, to the cruise control module to maintain that speed, to the ABS system via the wheel speed sensors to arm the brakes, traction -, and stability control systems, and to other affected controllers, such as the proximity alert control module to maintain a safe distance from other vehicles.
Although this example is a gross over-simplification of the CAN system, it should suffice to illustrate the complexity of the system. However, to complicate matters further, each control module is programmed with a set of messages it expects to receive from other control modules.
Thus, when a particular control module does not receive an expected signal, or when a particular control module detects a break in communication from one or more of the control modules it should be in contact with, a code is set, and in some cases a warning light will be illuminated. Note that some failures will set a code immediately, while others require several fault cycles before setting a code and illuminating a warning light.
The image below shows a hugely simplified representation of the major components and systems that are interconnected by the CAN bus system. Note that systems such as power window control and others that are typically controlled by the BCM (Body Control Module), are not shown here.