Auxiliary Heater Control, Checking

Auxiliary Heater Control, Checking

Only installed on vehicles with Diesel engine

- The data is exchanged with the auxiliary air heater control module (J604) , the auxiliary heater control module (J364) (of parking heater) or the respective Engine Control Module (ECM) over the CAN-Bus system. Check using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.

• 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 (J604) or from Engine Control Module -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 (VAS5051B) in "Guided Fault Finding" function (Guided Fault Finding for the respective ECM).

• 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 air heater heating element is via the auxiliary air heater control module. Check using Vehicle diagnosis, testing and information system (VAS5051B) 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 (Z35) is installed, which is actuated via a relay by the respective Engine Control Module (ECM).

• At this time, an Auxiliary Air Heater Heating Element (Z35) 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 (Z35) will be discontinued, then the parking heater undertakes the function of the auxiliary heater.

• Testing the electric auxiliary air heater activation in a vehicle with a auxiliary air heater control module (J604) is described in Guided Fault Finding for the A/C system of the Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.

• 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 (VAS5051B) in "Guided Fault Finding" function.

• Functional testing of the electric auxiliary air heater activation on a vehicle with a 3-stage auxiliary air heater heating element is described in Guided Fault Finding of the respective Engine Control Module (ECM) of the Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.

• At this time, no auxiliary heater is installed in vehicles with gasoline engine, also the parking heater is not activated as auxiliary heater.

Switch-On Criteria For Auxiliary Heater Activation

• On vehicles with A/C system, the switch-on requirements must be met in the Climatronic Control Module (J255) / or in A/C Control Module (J301) and in the respective Engine Control Module (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=> [ Auxiliary Air Heater Heating Element (Z35) Activation, Testing (Without A/C) ] Auxiliary Air Heater Heating Element (Z35) Activation, Testing (Without A/C).

- The Climatronic Control Module (J255) / A/C Control Module (J301) sends a request to switch on the auxiliary heater to the Auxiliary Air Heater Control Module (J604) , to the ECM or the Auxiliary Heater Control Module (J364) (of parking heater) in the event the following requirements are met:

• Engine is running for a minimum of 8 seconds and engine speed is greater than 500 RPM.

• Engine temperature is lower than 75 °C.

• The calculated outside air temperature is lower than 8 °C.

• The Stop function in the Start/Stop System is not active.

• Vehicle voltage supply is greater than 12.2 volts and no request that forbids the switch-on is sent by Vehicle Electrical System Control Module (J519).

• No DTCs are stored in Climatronic Control Module (J255) / A/C Control Module (J301).

• No DTC is stored in ECM and output of Generator (GEN) is less than 30 to 77% (depending on engine speed, this does not apply to activation of the parking heater as the auxiliary heater).

• Based on the setting and the temperatures measured, Climatronic Control Module (J255) / A/C Control Module (J301) has calculated that additional heat output is necessary to attain the intended passenger compartment temperature.

• More than 90% of air (position of temperature doors) is directed through heater core of heating & A/C unit for the left or right side.

• On vehicles equipped with a auxiliary air heater control module (J604) it controls the auxiliary air heater heating element (Z35) in such way so the load on the generator does not exceed 95%. Check using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.

• On vehicles with a 3-stage auxiliary air heater heating element (Z35) , 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 (VAS5051B) in "Guided Fault Finding" function (for ECM). Thus the next stage is switched on only in the event generator load is less than 30 to 77%, depending on engine speed.

Switch-Off Criteria For Auxiliary Heater Activation

• On vehicles with A/C system, activation is switched off as soon as one of the switch-on requirements in the Climatronic Control Module (J255) / or in A/C Control Module (J301) and in the respective Engine Control Module (ECM) is no longer met or one of the switch-off criteria is detected.

- The Climatronic Control Module (J255) / A/C Control Module (J301) switches off the request to switch on the electric auxiliary heater.

• When one of the switch-on requirements is no longer met.

• The calculated outside air temperature is higher than 11 °C.

• Generator (GEN) load is greater than 95%.

• Less than 60% of air is directed through heater core of heating & A/C unit for the left and right sides (position of temperature doors).

• On vehicles equipped with a auxiliary air heater control module (J604) it controls the auxiliary air heater heating element (Z35) in such way so the load on the generator does not exceed 95%. Check using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.

• On vehicles with a 3-stage auxiliary air heater heating element (Z35) , the Engine Control Module (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 (VAS5051B) in "Guided Fault Finding" function (for ECM). If the load on the generator exceeds 95%, then the output of the auxiliary air heater heating element (Z35) will be reduced by one third.