Air Conditioning Interfaces

Engine Control Module - IHKA Interface
- The engine control module - IHKA interface has been changed on the E39. The familiar interface including; S-AC, S-KO and S-KO-REL have been modified. S-AC and S-KO have been combined into one wire. S-KO-REL function is unchanged.
- The new S-KO is an input signal to the engine control module signifying IHKA system status. It is a PWM signal with changing duty cycle representing the various system changes.

NOTE: The duty cycle increases from 45 to 90% in steps. At present the engine control module only monitors the difference between 15, 30 and 45% to recognize IHKA system activity. Future engine control systems will utilize the additional load stage settings.

^ With KL 15 ON and the snowflake button not pressed, a 15% duty cycle is input to the engine control module.
^ When the snowflake button is pressed (LED ON) the duty cycle increases to 30%. This puts the engine control module into a standby mode in preparation for compressor on.
^ When the IHKA requires compressor activation the duty cycle increases to 45% - 90%. The engine control module prepares for the additional load of the compressor by increasing the idle speed and correcting the injection time.

- When the engine control module is ready for the compressor load, it signals the IHKA by pulling a standing voltage low (S-KO-REL).
- The ground is released when the ECM requires compressor deactivation.