Engine Management System Interface
Engine Management System Interface
Other interfaces
The DME control unit requires a number of other signals for engine management.
Brief description of components
The following components for the other interfaces are described:
Accelerator pedal module
The accelerator pedal module detects the position of the accelerator pedal. The DME control unit uses this to calculate the required position of the throttle valve, taking account of other factors.
The accelerator pedal module works according to the magnetoresistive principle. Two Hall sensors (rotational angle) are deployed to enable monitoring and fault recognition.
The two Hall sensors are supplied separately with 5 Volts and earth by the DME. The sensor signals are also transferred separately. The signals are transferred as analog.
The DME monitors the two input signals of the Hall sensors and compared these for plausibility.
Clutch module
On vehicles with manual gearboxes, the clutch module at the clutch pedal picks up the clutch position (clutch pressed: clutch switch open; clutch not pressed, clutch switch closed). The clutch module consists of a clutch switch and an electronic evaluation unit.
The clutch module is supplied with 12 Volts, terminal R, and earth. A signal line leads into the DME. When the clutch pedal is not pressed, the clutch module delivers 12 Volts to the DME, and when the clutch pedal is pressed it delivers 0 Volts.
Brake-light switch
Two switches are built into the brake-light switch: the brake-light switch and the brake-light test switch (redundancy for safety reasons). The signals indicate to the DME control unit whether the brake pedal has been pressed.
The brake-light switch is supplied with 12 Volts, terminal R, and earth. Two signal lines lead into the DME. When the brake pedal is not pressed, the clutch module delivers 0 Volts across a signal line to the DME, and when the brake pedal is pressed it delivers 12 Volts. The brake light test switch delivers the same signals to the DME.
Refrigerant pressure sensor
The refrigerant pressure sensor for the air conditioning system is located in the pressure line of the refrigerant circuit. In the cooling mode the refrigerant high pressure is picked via the pressure sensor are evaluated in the DME.
The refrigerant pressure sensor is supplied with 5 Volts and earth by the DME. The information is sent to the DME across a signal cable. The signal fluctuates depending in the pressure. The measuring range of approx. 0.1 to 0.9 Volts corresponds to a pressure of approx. 10 kPa (0.1 bar) to 3.5 MPa (35 bar).
The DME can use the signal of the pressure sensor and the stored characteristic map to calculate the pressure in the pressure line of the refrigerant circuit and, depending on requirements, switch the electric fan on or off.
The signal for switching the compressor clutch on or off is also sent across the PT-CAN to the junction box electronics (JBE).
DME control unit
New functions of the engine management system are:
- As of 08/2007: intelligent alternator control
- as of 08/2007: Automatic engine start-stop (see separate chapter)
There are 3 other sensors on the board in the DME control unit: a temperature sensor, an ambient-pressure sensor as well as a voltage sensor. The temperature sensor provides thermal monitoring of the components in the DME control unit. The ambient pressure is required for calculation of the mixture composition. The ambient pressure falls the higher you go above sea level. The voltage sensor on the board of the DME control unit monitors the power supply via terminal 87.
The DME control unit is connected with the vehicle electrical system via the engine wiring harness and vehicle wiring harness (3 connector chambers).
The DME control unit is connected via the PT-CAN (Powertrain CAN) across a gateway with the remaining bus system. The gateway is the junction box electronics (JBE).
System functions
The following system functions are described:
Electronic vehicle immobilization
The electronic immobilizer is both an anti-theft device and start enable device. On the MINI, a newly developed electronic immobilizer (4th generation) is introduced. This development uses a new and modern encryption method.
Each vehicle is assigned a 128-bit secret code. This secret code is stored in a BMW database. This means that the secret code is only known to BMW. The secret code is programmed and locked in the CAS control unit and the DME control unit. When the secret code is in the control units, it can no longer be deleted or changed. This means that each control unit is assigned to a certain vehicle. The CAS control unit and the EWS control unit mutually identify themselves with the secret number and the same algorithm.
If the identification data is correct, the CAS control unit activates the starter motor via a relay in the control unit. At the same time, the CAS control unit sends the DME control unit a coded enable signal (changing code) for the engine start. The DME control unit only enables the engine start if a correct enable signal is received from the CAS control unit. These procedures may result in a slight start delay (up to half a second).
Notes for Service department
General information
NOTE: Procedure in the event of a defective control unit.
If the CAS or DME is defective, a certain procedure must be followed.
The required control unit must be ordered exactly for the vehicle. For this, the vehicle data (vehicle identification number) is required.
An EWS adjustment is not necessary after renewing the control unit.
No liability can be accepted for printing or other errors. Subject to changes of a technical nature.