LIN bus in the integrated automatic heating and air conditioning system

Detailed functional description, see BMW Technology 6450xxxxx.xx

Notes on function

The LIN bus is a bidirectional, single-wire bus line. The IHKA operating unit supplies the components connected on the LIN bus. Only the IHKA operating unit asks a component to become active by means of a data message or to send information. The components connected to the LIN bus do not sending any data messages. The bus protocol is thus strictly and hierarchically divided into master controller and slave, whereby the IHKA operating unit is the master controller and the connected components are slaves.

LIN bus structure

The IHKA operating unit is connected to the components via three lines. Two lines provide the power supply; the third line is the data bus. The power supply for the components is 8 to 16 Volts and is provided by the IHKA operating unit.

All the flap motors and, depending on the engine variant, an electrical auxiliary heater are connected on the LIN bus. The blower output stage is also connected on the LIN bus, but connected via separate connections to the IHKA operating unit.

Notes on troubleshooting

Fault memory

The following faults can be recognized:

• E706 heating/air conditioning system LIN bus faults
  Fault detection: Which components respond to a data message from the IHKA operating unit on the LIN bus.
  Fault classes:
  
  • Only the electric auxiliary heater responds on the LIN bus
    Only the blower control responds on the LIN bus
    No component connected on the LIN bus responds
    
• Flap motors of the heating/air conditioning on the LIN bus
  Fault detection: The current consumption and the thermal load of the flap motor are monitored. The monitoring detects if a flap motor is not responding or is mechanically blocked.
  Fault classes:
  
  • Internal flap motor fault
    Flap motor blocked
    Flap motor does not respond on the bus system
    
• 9C57 blower output stage
  Fault detection: The current consumption of the blower motor is monitored. The monitoring detects if a blower output stage is not responding, if the blower motor is blocked, or if there is a line break or short circuit.
  Fault classes:
  
  • Blower motor current consumption too low
    Blower motor blocked
    The blower output stage does not respond on the LIN bus
    Line break or short circuit in the blower motor circuit
    
• 9C53 electrical auxiliary heater
  Fault detection: The current consumption of the electrical auxiliary heater is monitored. The monitoring detects if the electrical auxiliary heater is thermally overloaded, is not responding on the LIN bus or if there is a short circuit in one of the heating elements.
  Fault classes:
  
  • Thermal overload
    Short circuit in the heating element
    Does not respond on the LIN bus