Auxiliary Air Heater Heating Element (Z35) Activation, Testing (Without A/C)
Auxiliary Air Heater Heating Element (Z35) Activation, Testing (Without A/C)
Only installed on vehicles with Diesel engine
Special tools, testers and auxiliary items required
• Test Box 105 Pin (V.A.G 1598/42-1) and Test Adapter (V.A.G 1598/47)
• Vehicle Diagnostic, Testing and Information System (VAS 5051B) with Multimeter Leads (VAS 5051/7)
• 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 in the event there is a request from the heater controls ( Heater Control Module (J65) ). The electric auxiliary air heater is controlled by the Auxiliary Air Heater Control Module (J604) or by the engine control module (on the 3-stage version by the Low heat output relay (J359) and the High heat output relay (J360) ). Check using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding" (Guided Fault Finding for each engine control module).
• 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 via the auxiliary air heater control module. Check using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding". 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). Check using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding" (Guided Fault Finding for respective ECM).
• Functional testing of the electric auxiliary air heater activation on a vehicle with a auxiliary air heater control module (J604) is described in Guided Fault Finding of the A/C system using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding".
• 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) under "Guided Fault Finding".
• Functional testing of the electric auxiliary air heater activation on a vehicle with a 3-stage Auxiliary Air Heater Heating Element (Z35) is described in Guided Fault Finding of the respective ECM. Check using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding".
Check Activation Of Heater Controls ( Heater Control Module (J65) )
• The heater control module has a switch. This switch is operated (closed) via rotary switch for temperature preselect - A - in area from approximately 3 o'clock position up to "warm" stop.
- If the switch for the auxiliary heater is closed, then the electronics in the heater control module will switch through terminal 7 ground to the auxiliary air heater control module (J604) / to the respective engine control module with the ignition turned on. Auxiliary air heater control module / ECM detects that additional heating performance is desired and switches on the electric auxiliary heater when the other switch-on requirements necessary for activation have also been met.
• Switch-on conditions for electric auxiliary air heater (activation of auxiliary air heater heating element) from the auxiliary air heater control module. Check using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding".
• Switch-on conditions for electric auxiliary air heater (activation of auxiliary air heater heating element) from respective Engine Control Module (ECM). Check using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding" (Guided Fault Finding for respective ECM).
• In order for each engine control module to control the 3-stage auxiliary air heater heating element via the Low heat output relay (J359) and the High heat output relay (J360) , the engine control module must fulfill the same conditions, which are also required in the A/C control module (J301) on vehicles with a manual A/C system. Check using Vehicle diagnosis, testing and information system (VAS5051B) under "Guided Fault Finding".
Switch-On Criteria For Electric Auxiliary Air Heater Activation
- Engine Control Module (ECM) actuates auxiliary air heater heating element via Low heat output relay (J359) and High heat output relay (J360) in the event the following requirements are met:
• There is a Ground (GND) signal at ECM from Heater Control Module (J65).
• 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.
• 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 DTC is stored in ECM and Generator load is less than 30 to 77% (depending on engine speed)
• On vehicles with a 3-stage auxiliary air 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 (VAS5051B) under "Guided Fault Finding" (for ECM). Thus the next stage is switched on only in the event the Generator load is less than 30 to 77%, depending on engine speed.
Switch-Off Criteria For Auxiliary Heater Activation
• On vehicles without A/C system, activation is switched off as soon as one of the switch-on requirements is no longer met in Engine Control Module (ECM) or one of the switch-off criteria is detected.
• When one of the switch-on requirements is no longer met.
• The calculated outside air temperature is higher than 11 °C.
• Generator load is greater than 95%.
• There is no longer a Ground (GND) signal at ECM from Heater Control Module.