Diagnostics

Diagnostics

The ECM monitors the MFL serial link to check for faults with the interface ECU. The MFL signal contains a toggle bit which the interface ECU changes to a different state every second to indicate that the interface ECU is operating correctly and receiving a valid CAN bus signal. If a fault occurs with the CAN bus signal or the interface ECU, the toggle bit remains unchanged and the ECM interprets the unchanged toggle bit as a fault. If the interface ECU fails to output the MFL signal, the ECM also interprets the lack of a signal as a fault.

If a fault is detected, the ECM disables cruise control for the remainder of the ignition cycle and stores a related fault code in memory. The fault codes can be accessed using T4, which communicates with the ECM via an ISO 9141-2 K line from the diagnostic socket.

The ECM monitors the two inputs from the brake pedal position sensor and disables cruise control if a fault is detected. The ECM can detect open circuits and implausible inputs. However, simultaneous short circuits to 0 volt in both inputs cannot be detected and, if this occurs, cruise control operates but does not suspend operation when the brake pedal is pressed.

The ECM resets the cruise control system at the beginning of each ignition cycle and operates normally if a previously detected fault is no longer present.