Heating and Air Conditioning: Application and ID

On Board Diagnostic (OBD) Technical Data

Memory Permanent memory
Data output "Rapid data transfer" operating mode 1
On Board Diagnostic (OBD) "AC/Heating Electronics" address word 08
Check Control Module Versions Function 01
Check DTC Memory Function 02
Output Diagnostic Test Mode Function 03
Basic Setting Function 04
Erase DTC Memory Function 05
End Output Function 06
Code Control Module Function 07
Read Measuring Value Block Function 08


NOTE:
- If a newly installed the A/C control head -E87- has not been coded or an invalid code has been entered in the A/C control head -E87-, the coding "00001" will be stored.
- If a new A/C control head -E87- is installed, and its display panel flashes (for about 2 minutes) when the ignition is switched on, code the A/C control head -E87- (function 07) and perform basic setting (function 04).
- While the On Board Diagnostic (OBD) is performed, the control functions of the air conditioner remain in operation and are not switched off (i.e. the compressor, positioning motors, coolant fan etc. can be activated).
- When the OBD is started, the control functions of the air conditioner are not interrupted. However, they are switched off if the output diagnostic test mode or basic setting functions are selected. If other diagnostic functions are selected, the air conditioning remains fully functional.
- The A/C control head -E87- is no longer connected to terminal 30 of the electrical system; it stores its latest setting when the ignition is switched off, and then reactivates it when the ignition is switched on again.
- The time which has elapsed since the ignition was switched off is calculated by the A/C control head -E87- when the ignition is switched back on (time signal supplied by instrument cluster). If more than 4 hours pass after the ignition is switched off, the current measured values from the outside air temperature sensors are used to represent the current ambient temperature and engine temperature for the purposes of regulating the system. If the "standing time" was less than 4 hours, the current values are calculated by the A/C control head -E87- (the heat emitted from the engine and radiator causes incorrect measurements, and therefore the current measured values from the temperature sensors are suppressed for a predefined time).
- The lower of the two values from the outside air temperature sensors is used for air conditioning regulation and for the external temperature display.
- When the convertible top is opened on Audi TT Roadsters, A/C regulation is altered. Instead of using the measured value from instrument panel interior temperature sensor -G56-, the system assumes pre-programmed outlet temperature values based on the current outside temperature. -E87- receives this information via terminal 5 in connector C from convertible top control module -J256-.


On Board Diagnostic (OBD), Test Requirements

- All fuses OK per wiring diagram.
- Battery voltage OK.
- For testing, ignition must be switched on or the engine running (engine speed less than 3000 rpm).