Vehicle Identification
Vehicle ID is carried out on the basis of control module data (EWS and IKE/Cluster ZCS) For automatic ID, the DIS or MoDiC reads the ZCS code to determine what systems are installed in the vehicle and directly seeks them out. This process is much faster than previous method of polling all systems possible for a specific vehicle series. If the "D" bus is faulted or the tester can not communicate for whatever reason, manual ID is required.
When either manual or automatic vehicle identification has been completed, the VEHICLE SYSTEM screen appears. The brief test must be carried out before diagnosis can take place. Carry out the brief test to interrogate the fault memories of all control systems. The system contacts the control modules directly to check if the control module is installed and capable of communication. The status of the control module is then displayed in the Vehicle ID screen. Another option is to check control modules for individual interrogation by pressing the systems individually from the screen. Correct vehicle identification is the first essential step for both system guided and user guided troubleshooting.
Integral Electric Throttle System (EML) Functional Description
When the accelerator pedal is moved, the PWG provides a change in the monitored signals. The X5 ME 7.2 compares the input signal to a programmed map and appropriately activates the EDK motor via proportionally high/low switching circuits. The control module self-checks its activation of the EDK motor via the EDK feedback potentiometers. (Scheme 1) Requirements placed on the Electric Throttle System (EML)
- Regulate the calculated intake air load based on PWG input signals and programmed mapping.
- Control idle air with regard to road speed as per previous systems.
- Monitor driver's input request for cruise control operation.
- Automatically position EDK for accurate cruise control operation.
- Perform all DSC III throttle control interventions.
- Monitor and carry out maximum engine and road speed cutout.
Scheme 1
PWG Signal Monitoring & PWG Failsafe Operation
As a redundant safety feature the PWG provides 2 separate signals from 2 integral potentiometers (pot 1 and pot 2) representing the driver request for throttle activation. If the monitored PWG potentiometer signals are not plausible, ME 7.2 will only use the lower of the 2 signals as the driver's pedal request input, providing failsafe operation. Throttle response will be slower and maximum throttle position will be reduced. When in PWG failsafe operation, ME 7.2 sets EDK throttle plate and injection time to idle whenever brake pedal is depressed. When the system is in PWG failsafe operation, the instrument cluster matrix display will post ENGINE EMERGENCY PROBLEM and PWG specific fault(s) will be stored in memory.
EDK Feedback Signal Monitoring & EDK Failsafe Operation
The EDK provides 2 separate signals from 2 integral potentiometers (pot 1 and pot 2) representing the exact position of the throttle plate. EDK pot No. 1 provides the primary throttle plate position feedback. As a redundant safety feature, pot No. 2 is continuously cross checked with pot No. 1 for signal plausibility. If plausibility errors are detected between pot No. 1 and pot No. 2, ME 7.2 will calculate the inducted engine air mass (from HFM signal) and only utilize the potentiometer signal that closely matches the detected intake air mass. The ME 7.2 uses the air mass signalling as a virtual potentiometer (pot No. 3) for a comparative source to provide failsafe operation. If ME 7.2 cannot calculate a plausible conclusion from the monitored pots (1 or 2 and virtual 3) the EDK motor is switched off and fuel injection cut out is activated (no failsafe operation possible).
The EDK is continuously monitored during all phases of engine operation. It is also briefly activated when motor is initially switched on as a pre-flight check to verify its mechanical integrity (no binding, appropriate return spring tension, etc). This is accomplished by monitoring both the motor control amperage and the reaction speed of the EDK feedback potentiometers. If faults are detected, the EDK motor is switched off and fuel injection cut off is activated (no failsafe operation possible). The engine does, however, continue to run extremely rough at idle speed. When a replacement EDK is installed, the ME 7.2 adapts to the new component (required amperage draw for motor control, feedback pot tolerance differences, etc). This occurs immediately after the next cycle for approximately 30 seconds. During this period of adaptation, the maximum opening of the throttle plate is 25 percent.
Siemens is an engine management system which meets the needs of Low Emission Vehicle (LEV) compliancy and is also OBD II compliant. This system also includes control of the Motor-Driven Throttle Valve (MDK). The PCM uses a pc-board single-processor control unit in the new SKE housing. E-box is located next to brake master cylinder. The Siemens PCM is flash programmable as are previous systems. PCM hardware includes
- Modular plug connectors featuring 5 connectors in the SKE housing with 134 pins.
- Connector 1 = Supply voltages and grounds.
- Connector 2 = Peripheral signals (oxygen sensors, CAN, etc.).
- Connector 3 = Engine signals.
- Connector 4 = Vehicle signals.
- Connector 5 = Ignition signals. Special features include flash EPROM which is adaptable to several M52 LEV engines and has the capability to be programmed up to 13 times. Once a control unit is installed and coded to a vehicle it cannot be swapped with another vehicle for diagnosing or replacement. A new PCM must be installed if necessary.
MDK Emergency Operation
If a fault is detected in the system, the modes of operation are emergency operation 1 and emergency operation 2.
Emergency operation 1 involves activation of the EML warning lamp, MDK deactivated, the throttle valve is opened mechanically by the springs and throttle cable, MDK opening is compensated for by closing the idle speed actuator and retarding the ignition (engine power reduction) and engine power is further limited by fuel injector cutout. Emergency operation 1 limits the dynamic operation if one or more of the potentiometers fail. The engine can slowly reach maximum speed with limited power. The EML light will be illuminated to alert the driver of a fault.
If another fault is encountered in addition to emergency operation 1 or if the plausibility is affected, emergency operation 2 is activated by the PCM. An example of plausibility fault would be that the pulley position does not match the MDK position and the associated airflow. Emergency operation 2 can also be initiated by simultaneously pressing both the accelerator pedal and the brake pedal, or if a fault is encountered in the brake light switch diagnosis. When in emergency 2 operation mode, there is an engine speed limitation (slightly above idle speed) in addition to the measures for emergency operation 1. In emergency operation 2, the engine speed is always limited to 1300 RPM if the brake is not applied, and approximately 1000 RPM if the brake is applied. The vehicle speed is limited to approximately 20-25 mph. The reason for limiting the vehicle speed is if the MDK is wide open and vacuum assist is insufficient for the brakes. The emergency operation functions are inactive when ignition is switched off, main relay is deactivated, and engine is started again.
MDK safety concept can detect a jammed or binding throttle valve as well as a broken link spring. This fault is detected by the PCM monitoring the feedback potentiometers from the MDK in relation to pulse width modulation to activate the MDK motor. Emergency operation functions if the throttle valve is jammed. In the event of a fault, the DIS or MoDiC must be used to interrogate the fault memory, and clear the fault once the proper repair has been performed.
DC Motor LDP Inactive - Normal Purge Valve Operation
In its inactive state the pump motor and the change over valve of DC Motor LDP are not energized. When purge valve operation occurs filtered air enters the fuel system compensating for engine vacuum drawing on the hydrocarbon vapors stored in the charcoal canister.
See also:
• WIRING DIAGRAMS