Engine Control Module - IHKA Interface

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.