Examples of defective CAN-Bus signals

Fig 1: Defective CAN-Bus Signals (1 Of 4)

Courtesy of BMW OF NORTH AMERICA, INC.

This example represents the output signal produced by an AGS module that is isolated from the bus. This pattern times out after 10 seconds and remains a flat line at 2.5 volts until the key is cycled and the event is repeated.

Fig 2: Defective CAN-Bus Signals (2 Of 4)

Courtesy of BMW OF NORTH AMERICA, INC.

If a continuous flat line is present at one or both CAN lines of a particular control unit, this may indicate that the CAN is open to that particular module. The module may have timed out and is waiting for a signal from another control unit. Check the CAN-Bus at other points to see if communication is occurring else where on the bus.

Fig 3: Defective CAN-Bus Signals (3 Of 4)

Courtesy of BMW OF NORTH AMERICA, INC.

All of the other control units with the exception of most current AGS modules will continue to try and send information even though the control unit has already stored a "Timeout" or CAN fault. This type of signal may only be seen if a section or all of the CAN-Bus is disconnected.

Fig 4: Defective CAN-Bus Signals (4 Of 4)

Courtesy of BMW OF NORTH AMERICA, INC.

If the CAN-Bus lines were to become shorted to one another then the signals would cancel each other out and effectively be a flat line.