Auxiliary Heater Control, Checking

• An electric auxiliary air heater is currently installed in vehicles with diesel engine. In this system, the air is supplied with heat energy after it has left the heater core of the heater / A/C unit, in the event a request from the Climatronic Control Module -J255- / or from the A/C Control Module -J301- is present. Activation of electric auxiliary air heater occurs from Auxiliary Air Heater Control Module or from ECM (on the 3-stage version, via Low Heat Output Relay -J359- and High Heat Output Relay -J360-). Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in the "Guided Fault Finding" function (Guided Fault Finding for the respective ECM) and refer to the appropriate SYSTEM WIRING DIAGRAMS information.
• The electric auxiliary air heater is available in different versions. On vehicles equipped with a diesel engine built through November 2006 (running change) the control of the Auxiliary Heater Heating Element -Z35- via the Auxiliary Air Heater Control Module -J604-. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function. On vehicles with Diesel engine manufactured later than November 2006 (running change in production), a 3-stage Auxiliary Air Heater Heating Element is installed, which is actuated via a relay by the respective ECM. Refer to the appropriate SYSTEM WIRING DIAGRAMS information.
• At this time, an Auxiliary Air Heater Heating Element is also installed in vehicles with Diesel engine and parking heater as optional equipment. At a later point in time (not yet finalized), the Auxiliary Air Heater Heating Element will be discontinued, then the parking heater undertakes the function of the auxiliary heater.
• Functional testing of the electric auxiliary air heater activation on a vehicle with a Auxiliary Air Heater Control Module is described in Guided Fault Finding of the A/C system using Vehicle Diagnosis, Testing and Information System VAS 5051.
• Measuring value block of auxiliary air heater control module indicates that auxiliary heater is switched on or why no activation is occurring despite a request. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
• Functional testing of the electric auxiliary air heater activation on a vehicle with a 3-stage auxiliary heater heating element is described in Guided Fault Finding of the respective Engine Control Module (ECM) using Vehicle Diagnosis, Testing and Information System VAS 5051.
• From MY 2010, this vehicle has a Start/Stop System for specific engines as optional equipment. On vehicles with the Start/Stop System. the auxiliary heater heating element is switched off when the Stop function is active (to protect the battery). After the engine started with the Start function, the auxiliary heater heating element is switched on again. Refer to Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
• At this time, no auxiliary heater is installed in vehicles with gasoline engine, also the parking heater is not activated as auxiliary heater.

• On vehicles with A/C system, the switch-on requirements must be met in the Climatronic Control Module / or in A/C Control Module and in the respective ECM.
• On vehicles without A/C system (with heater only), the switch-on criteria must be met in the ECM and the Heater Control Module -J65- must connect through Ground (GND) as the switch-on signal, refer to TESTING AUXILIARY HEATER ACTIVATION, WITHOUT A/C .

• On vehicles equipped with a auxiliary air heater control module it controls the auxiliary heater heating element in such way so the load on the generator does not exceed 95%. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
• On vehicles with a 3-stage auxiliary heater heating element, the ECM actuates both relays for auxiliary heater in such a way that generator load does not exceed 95% Check using Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding" (for ECM) and refer to the appropriate SYSTEM WIRING DIAGRAMS information. Thus the next stage is switched on only in the event the generator load is less than 30 to 77%, depending on engine speed.

On vehicles with A/C system, activation is switched off as soon as one of the switch-on requirements in the Climatronic Control Module / or in A/C Control Module and in the respective ECM is no longer met or one of the switch-off criteria is detected.

• On vehicles equipped with a auxiliary air heater control module it controls the auxiliary heater heating element in such way so the load on the generator does not exceed 95%. Check using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
• On vehicles with a 3-stage auxiliary heater heating element, the ECM actuates both relays for auxiliary heater in such a way that the generator load does not exceed 95%. Check using Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding" => (for ECM) and refer to the appropriate SYSTEM WIRING DIAGRAMS information. If the load on the generator exceeds 95%, then the output of the auxiliary heater heating element will be reduced by one third.