Reading and Clearing Diagnostic Trouble Codes
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 this publication include:
- KTS300 "HAMMER" by Robert Bosch
- 5520 BMW ENGINE DIAGNOSTIC TOOL by Assenmacher Special Tools (AST)
- CARSOFT BMW DIAGNOSTIC SOFTWARE by Krahe
NOTE: Since typical diagnostic testers usually have differences in diagnostic capabilities, 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 Transmission Control (EGS) 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 are 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 a control unit detects defects provided the necessary conditions have been fulfilled (time, temperature, load etc.). However, defects can only be registered when there is an electrical connection to the control unit. If this is not the case, the check must be performed using conventional methods.
Diagnostic Trouble Code Storage
By way of plausibility checks and checking the line connections for shorts or breaks, the control unit can detect and store defect codes after the engine has been started. 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.
If the defect code memory has no defect code stored although there is a defect in the vehicle, either the test conditions (e.g. temperature, time, load etc.) for defect detection were not fulfilled or it was technically not possible to store a defect code.
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 Electronic Transmission Control (EGS) system operation may lead to misdiagnosis and needless expense. Always review Description and Operation. Description and Operation
The learned adaptation values are lost if the battery or the EGS control unit is disconnected. This may result in abrupt or altered shift points. These problems are generally rectified after a test drive.
Clearing the Diagnostic Trouble Code Memory
Carry out this function when directed by test instructions or when defects can be attributed to simulation. When the battery or the EGS control unit are disconnected, all stored defect codes and substitute values (if active) as well as the adaptation values are lost.
Diagnostic System Quick Test
The system quick test or "interrogation" surveys all systems which have Diagnostic Trouble Code (DTC) capabilities and should be used to verify that other systems are operating correctly. Defects in Digital Motor Electronic (DME) and other interelated systems can effect the Electronic Transmission Control (EGS) system.
Diagnostic Trouble Code (DTC) Memory Inquiry
Systems which have been identified as containing DTC's during the system quick test require further interrogation. If several defect codes are stored, interrelationships can often be deduced, indicating whether the defect can be attributed to central causes. Be sure to follow instructions and perform all tests as may be specified by the diagnostic tester.
Diagnostic Trouble Codes (DTC) Tests
DTC test instructions explain and supplement the self-diagnostic system and scan tool error messages.
The number of the defect code points to circuits identified by pin assignments at the control unit. 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, they 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. Transmission Control System
NOTE: Troubleshooting without a thorough understanding of EGS 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
Status Monitoring (Data Stream)
Inputs and outputs can be monitored independently of the defect code storage function. In this case, current values or operating statuses are displayed.
Component Activation
To facilitate fast fault finding, various components can be activated by the diagnostic equipment in conjunction with the EGS control unit. The response of components in perfect working order, including their supply lines, can therefore be indicated by acoustic and electrical means.
Irrespective of whether DTC's are stored or not, status monitoring and component activation should always be used for fault tracing.
CAUTION: Disconnect control units from the wire harness only with the ignition switched "Off". After renewed operation, neutral basic values are set in the control unit. Any irregularities in shift patterns can be corrected by means of renewed adaptations (new learned values) during a test run, in which an engine temperature of >176°F (>80°C) is reached.
The 88, 35 or 55-pin universal adapter or equivalent should be used for picking-off signals from the EGS control unit and from the engine wire harness. Perform wire checks only with the control unit or component connectors disconnected. Furthermore, the universal adapter should only be connected between the control unit and wire harness when no diagnostic procedure (diagnostic connector not connected) is to be carried out since this can lead to malfunctions.