Independent Heating Functions (SHZH Independent / Auxiliary Heater)

Functional description, independent heater

The independent heater (SH) is an integral part of the integrated heating and air-conditioning system. The SH provides heat output inside the vehicle that is not dependent on the engine. The control module is fitted directly on the heater. Communication in the overall vehicle takes place by means of K-CAN telegrams based on KWP 2000. The SH takes over activation of the components necessary for operation shown in the brief description of components.

Brief description of components

Independent heater control module
The function of the SH control module must be ensured when the voltage supply is applied. The activation (switching on and off) always takes place in normal operation via K CAN telegram. The control module is the central component and it communicates alongside the independent heating components with the DME/DDE, the CAS, the IHKA and the instrument cluster, which jointly ensure the correct operating mode of the independent heating. The control module consists of the control module, the temperature sensor, the overheating protection, the heat conductor and the connecting strip. The control module is vented by the combustion-air chamber of the burner via an air hose. Together with the burner housing, the control module forms a single unit and must not be disassembled.

Burner housing
The burner housing contains a coolant inlet and outlet and the exhaust-gas outlet connection. The burner housing accommodates the burner insert and together with the control module forms a single unit.

Combustion-air fan unit
The combustion-air fan unit contains the combustion-air fan, the opening for the fuel line and the opening for the fuel supply connection. The combustion-air fan delivers the air needed for combustion to the burner insert.

Burner insert
The fuel is distributed in the burner tube in the burner insert. Combustion of the fuel/air mixture takes place in the burner tube.

Heater plug/flame monitor
The heater plug/flame monitor located in the burner insert ignites the fuel-air mixture when the heater is started. After starting, heater plug/flame monitor takes on the task of the flame monitor. The heater plug/flame monitor is an electrical resistor. When the heater plug/flame monitor is active, there is cyclical static monitoring of the heater plug resistance. -> Heater-filament breakage detection.

Circulation pump (water pump of the independent heater)
The circulation pump is attached to the combustion air blower unit. The circulation pump ensures a flow of coolant in the vehicle/heater circuit. The pump is activated by the control module and runs throughout the entire operation of the independent heater. In the event of repairs, the circulation pump can be replaced separately.

Metering pump (fuel metering pump of independent/auxiliary heater)
The metering pump serves to supply the fuel from the vehicle's fuel tank. In the event of repairs, the metering pump can be replaced separately.

Changeover valve
The changeover valve switches between two separate water circuits: the engine coolant circuit and the independent heater circuit. At zero current, the changeover valve is set to the engine coolant circuit. In the event of repairs, the changeover valve can be replaced separately.

Integrated automatic heating/air conditioning
The independent/auxiliary heater is an integral part of the IHKA integrated heating and air-conditioning system. The IHKA controls the independent/auxiliary heater in all operating modes.

Digital Motor/Diesel Electronics
The Digital Motor/Diesel Electronics DME/DDE transmits cyclically every 200 ms the engine operating state engine on or off, which is evaluated by the auxiliary/independent heater.

Car Access System
The Car Access System CAS transmits cyclically every 500 ms the terminal status e.g. terminal R, terminal 15, which is evaluated by the independent/auxiliary heater.

Central Gateway Module
The Central Gateway Module (ZGM) connects the byteflight, K-CAN, PT-CAN data buses and the diagnostic bus.

Remote control for independent-heating functions
The independent-heating functions are activated by pressing the buttons on the remote control. In turn, the functions are actually executed by means of IHKA telegrams to the auxiliary/independent heater.

Function

Implausibility
When criteria are identified which call for the independent heater to be deactivated, it is first necessary to wait for the IHKA OFF command. Therefore, in this case, the independent heater starts a codable timer (default value: 10 seconds) within which the signal IHKA OFF must come. If it does not come, the independent/auxiliary heater switches off automatically and sends its status "Off due to implausible operating mode". This must be acknowledged by the IHKA (integrated automatic heating / air conditioning system) to enable a new start.

Independent heating, gasoline/gasoline and diesel
For independent heating, the outside temperature must lie below 16 degree C in the case of preselected switching time. Direct switching on via the Control Display is possible at all times.

Switch-on conditions (each of the following points must be satisfied - AND condition)
- Telegram switch on SH (telegram comes from the IHKA and can be triggered by a preselected switch-on time at the Control Display, direct operation selection at the Control Display, Telestarter.)
- No fault
- No fault lockout of heater
- Engine OFF
- Range for fuel quantity more than 50 kilometers

Switch-off conditions (each of the following points necessitates switching off of the independent-heating procedure or prevents switching on - OR condition)
- Telegram switch off SH (telegram comes from the IHKA and can be triggered by Control Display, direct operation deselection at the Control Display, telestarter, heating time elapsed)
- Fault
- Heating time elapsed (usually 30 minutes)
- 10 seconds implausibility (see Implausibility with independent heating)
- Undervoltage detected

Implausibilities / criteria (each of the following points necessitates switching off of the independent-heating procedure - OR condition)
- Status, engine running
- Operating mode not equal to independent heating
- Deactivation of stationary consumers by power module
- Undervoltage

Service functions

Overheating lock
In the event of a temperature-control failure or partial overheating, e.g. as a result of a lack of water, the overheating protection switches off the independent/auxiliary heater permanently. If the overheating lock is activated, an entry is made in the fault memory of the independent/auxiliary heater.

Heater lock
The independent/auxiliary heater is permanently locked if three malfunctions or three faults relevant to operation have occurred in sequence - i.e. without correct operation in between. For example, lack of fuel on a number of occasions could lead to failure to generate a flame. Here, the heater lock is activated, which leads to an entry in the fault memory of independent/auxiliary heater. This fault is not identical to the overheating lock fault.

Fault
The fault lockout occurs when a fault is detected during operation and the independent/auxiliary heater switches off.

Restart
- Fault
It only needs to be switched OFF once to cancel the fault lockout. It can then be restarted.
- Heater lock
The heater lock is unlocked using the service function "Unlock independent/auxiliary heater" AND then by pulling the fuse of independent/auxiliary heater (disconnecting the power).

Country and coding versions

Country versions
No country versions present.

Coding versions
The independent/auxiliary heater is coded once at the factory. A distinction is made between gasoline and diesel coded independent/auxiliary heaters. The independent/auxiliary heater cannot be coded in the dealer organization.