DME M3.3 Changes

DME M3.3 Changes












The function of DME M3.3 for the 740i/iL (E38) has been slightly changed as compared to the M3.3 system of the E32 M60. The differences are in the following areas:

- IHKA/DME system interface.
- Headlights on input deleted

IHKA/DME Interface
E38 DME M3.3 does not activate the AC compressor as did the E32 M60 M3.3. The E38 IHKA is now the controller of the compressor clutch.

- DME receives signal KO (12 volts standing - active when pulled low) from IHKA when the driver of the vehicle presses the "snowflake" button. DME surveys the status of the following:

- Engine speed
- Engine load
- Vehicle speed.

When all conditions are acceptable for AC compressor operation, DME increases the engines idle by controlling the idle control valve in preparation of the AC compressor activation. Simultaneously it sends the signal KO REL (12 volts) to IHKA.

IHKA perceives the KO REL signal as an "OK" to activate the AC compressor clutch. DME maintains the 12 volt signal but pulls it low when it requires the compressor to be cut out for the following condition.

- Vehicle speed < 10 MPH
- Full Throttle

The compressor cut out is for a maximum of 10 seconds.

When the IHKA control module applies operating power to the compressor clutch solenoid it also supplies a 12 volt high signal to the DME for acknowledgement of compressor operation.