Auxiliary Heater Activation, Checking (The Auxiliary Heater Heating Element -Z35-)
The components involved with the actuation of the auxiliary heater:
The air is supplied with heat energy via the Auxiliary Heater Heating Element -Z35- after it has left the heater core of the heater. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function. A prerequisite for this is a request from the control head, the Heater Control Module -J65- (vehicles without an A/C system), the A/C Control Module -J301- (vehicles with manually regulated A/C system), the Climatronic Control Module -J255- (vehicles with Automatic climate control).
The actuation of the Auxiliary Heater Heating Element -Z35- is switched off when the start/stop function is active to protect the Battery -A- on vehicles with the Start/Stop System. As soon as the engine is started via the start function, the Auxiliary Heater Heating Element -Z35- is reactivated. Use the :Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
At his time on vehicles with a high voltage system the Auxiliary Heater Heating Element -Z35- is not installed, on these vehicles the High Voltage Heater (PTC) -Z115- (with High Voltage Heater (PTC) Control Module -J848-) performs this function. Refer to HIGH VOLTAGE HEATER (PTC) -Z115- GENERAL INFORMATION, (AND TO THE HIGH VOLTAGE HEATER (PTC) CONTROL MODULE -J848-) .
Switch-on Criteria for Auxiliary Heater Heating Element -Z35- Actuation
- The switch on conditions must be fulfilled in the control head (Heater Control Module -J65-, A/C Control Module -J301- or Climatronic Control Module -J255-) and in the engine control module.
The control head (Heater Control Module -J65-, A/C Control Module -J301- or Climatronic Control Module -J255-) sends a request to switch on the auxiliary heater to the engine control module when the following requirements are met:
- The "Automatic auxiliary heater" is not deselected (indicator in the radio or MMI display). Refer to the Vehicle Owner's Manual.
- Engine is running for a minimum of eight seconds and engine speed is greater than 500 rpm.
- Engine temperature is lower than 75 °C (167 °F).
- The calculated outside air temperature is lower than 6 °C (42.8 °F).
- The stop function of the Start/Stop System is not active.
- The electrical system voltage 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 the control head (Heater Control Module -J65-, A/C Control Module -J301- or Climatronic Control Module -J255-).
- No DTCs are stored in the engine control module and the Generator -C- load is less than 30 to 77% (depending on the engine control module version). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
- Based on the setting and the measured temperatures, the control head (Heater Control Module -J65-, A/C Control Module -J301- or Climatronic Control Module -J255-) has calculated that additional heat output is necessary to reach the intended passenger compartment temperature.
- More than 90% of air (position of temperature doors) is directed through the heater core for the heater for the left or right side.
The engine control module actuates the Auxiliary Heater Control Module -Z35- via the Low Heat Output Relay -J359- and the High Heat Output Relay -J360- so that the Generator -C- load does not exceed 95%. The next stage is switched on only in the event that the generator load is less than 30 to 77%, depending on the engine speed. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function and Wiring diagrams, Troubleshooting & Component locations.
Switch-Off Criteria for Auxiliary Heater Activation
The actuation is switched off as soon as the "Automatic auxiliary heater" function is deselected (indicator in the radio or MMI display). A switch-on requirement is no longer met in the control head (Heater Control Module -J65-, A/C Control Module -J301- or Climatronic Control Module -J255-) or in the engine control module, or one of the switch off criteria has been detected.
The control head (Heater Control Module -J65-, A/C Control Module -J301- or Climatronic Control Module -J255-) switches off the request to turn on the electric auxiliary heater under the following conditions:
- One of the switch-on requirements is no longer met.
- The calculated outside air temperature is higher, about 8 °C (46.4 °F).
- The Generator -C- load is greater than 95%.
- Less than 60% of air is directed through heater core for the heater for the left and right sides (position of temperature doors).
- The stop function of the Start/Stop System is active.