Important Notes Concerning BMW Diagnostics (Start Here)
BMW SELF DIAGNOSTICSDiagnostic Equipment
In addition to the BMW Service Tester and the Mobile Diagnostic Computer (MoDIC), various manufacturers have produced diagnostic equipment compatible with BMW diagnostic systems. Although some differences exist between the range of capabilities, procedures and displays, these testers are capable of identifying BMW Diagnostic Trouble Codes (DTC), providing data stream information, and typically suggest some direction for remedy of the problem. Equipment recognized at the time of the publication include:
- KTS300 "HAMMER" by Robert Bosch
- 5510 BMW ENGINE DIAGNOSTIC TOOL by Assenmacher Special Tools (AST)
- CARSOFT BMW DIAGNOSTIC SOFTWARE by Krahe
NOTE: Typical diagnostic testers usually have differences in diagnostic capabilities. Therefore, application of the information presented in this section may vary. Always follow the directions provided by the equipment manufacturer.
Initialization of Diagnostic Procedure
Communication with the Electronic Throttle Control (EML) and other vehicle control units can be established with the use of a Diagnostic Scan Tool.
If data transfer is interrupted, information appears on the display screen indicating the possible cause:
- Ignition not switched on
- Voltage supply for control unit < 10 V
- Control unit not connected
- Diagnostic link defective
- Data traffic inhibited by a defective control unit in the vehicle
Control Unit Identification
If necessary, the control unit can be quickly identified with the aid of these data (factory requirement). Automatic allocation of the diagnostic programs is also based on these control unit numbers.
Effective Range of the Self-Diagnosis Function
The self-diagnosis function is an aid to facilitate fast fault tracing in the vehicle's electronic systems. The BMW MoDiC or equivalent tester provides the necessary access for the user. Self-diagnosis of the control units detects defects provided the necessary conditions for this have been fulfilled (time, temperature, load etc.). However, defects can only be registered when there is an electrical connection to the control unit.
Diagnostic Trouble Code Storage
Defect codes are stored after the ignition has been switched "ON". If several defects are detected, they appear in the order they first occurred.
The operating conditions as stored apply only to the conditions, under which the defect was detected for the first time. An intact voltage supply (battery charged) is the prerequisite for maintaining the memory contents.
The EML control unit stores a maximum of 5 defect codes. When the defect code memory is full, a new defect code with higher priority displaces an already existing defect code with lower priority.
NOTE: The component functions and signals listed below are processed or controlled by the EML control unit but not stored in the case of defect:
- LL-signal (sends "idle" information to the Digital Motor Electronic [DME])
- VL-signal (sends "full load" information to the DME)
- Kick-down switch
- Air conditioning switch
- A/C compressor clutch (relay output)
- Gear selector switch ("P" or "N" position in automatic transmission)
- Clutch switch (manual transmission)
- Brake light switch
- External safety path
Diagnostic Trouble Code Memory Interrogation
The first step should always be to monitor the defect code memory. If one or several defect codes are stored, it is advisable to record these data immediately. Since it is often necessary during the testing procedure to cut the power supply or to disconnect the connector from the control unit, the contents of the defect code memory will be unintentionally deleted as a consequence.
NOTE: Troubleshooting without a thorough understanding of EML system operation may lead to misdiagnosis and needless expense. Always review the Description and Operation provided at the system and component levels and systematically follow the test instructions. Specialized training and diagnostic test equipment are recommended. Description and Operation
Diagnostic Trouble Codes (DTC) Tests
DTC test instructions explain and supplement the self-diagnostic system or scan tool error messages.
The defect can be in the vicinity of the component, the corresponding wiring or in the control unit. If defects occur for which no DTC is stored, these tests provide the opportunity of performing troubleshooting with the aid of the subsequent tests. Electronic Diagrams should always be used since they clearly show the interaction of various components. Engine Control System
Defect Location
The defect can be in the vicinity of the component, the corresponding lines or in the control unit.
Defect Type
Range faults or illogical functions are detected.
Detected At
Provides additional information relating to the operating statuses during defect detection (compare values to substitute values). This information can provide an indication relating to the plausibility (in correct sequence), short-circuits, breaks in circuits or range faults.
Status Monitoring
Since not all inputs and outputs and their plausibility are covered by the defect code memory of the EML control unit, the status monitoring function (data stream) must also be used for successful troubleshooting.
The nominal values and actual values specified in the status lists need not agree exactly. If the deviation between the nominal value and actual value is outside the permissible range, then the EML control unit stores this as a defect.
The permissible ranges are specified in the functional Description and Operation or in the Diagnostic Trouble Code (DTC) Tests. When the permissible range is exceeded and the EML control unit has detected this as a defect, the actual value can be used to check the component and its system of lines without the need for extensive measurements.
Clearing the Diagnostic Trouble Code Memory
Carry out this function according to scan tool instructions only when all defects have been rectified or attributed to simulation. When the battery, instrument cluster or the EML control unit are disconnected, all stored defect codes and substitute values (if active) as well as the adaptation values are lost. Current defects (Hard) cannot be cleared before remedy of the problem is accomplished.