BMW Diagnostic System
DIAGNOSTIC SYSTEM
General
A large number of control units with self-diagnosis capabilities is used in the 3 Series (E36). In addition to the control of the relevant system, these control units are capable of making available or receiving data for diagnostic procedures. The data can be read out or entered with the BMW DIAGNOSTIC SYSTEM.
The data exchange between the control unit and the BMW DIAGNOSTIC SYSTEM takes place via 2 diagnostic links (RxD and TxD). The diagnostic links are combined in the diagnostic socket (Pin 15 RxD, Pin 20 TxD) where they can be connected to the BMW SERVICE TESTER or the BMW MoDiC.
To avoid faults occurring during vehicle operation, the RxD link is connected to battery voltage and the TxD link to ground when the diagnostic socket is closed.
After the tester disks have been loaded, the general overview of control units appears on the display screen. The diagnostic procedure is initiated by selecting the relevant control unit and the corresponding diagnostic program is assigned from the tester disk.
DIAGNOSTIC FUNCTIONS
Note
Important information on the control unit or on the diagnostic procedure can be called up from any screen page by way of the note button.
Read Defect Code Memory
The majority of control units are capable of automatically detecting a defect and to store it permanently. The contents of the defect code memory can be read out with the BMW DIAGNOSTIC SYSTEM. Additional information is, in part, also stored when a defect code is stored. This additional information indicates the operating conditions under which the defect occurred. More extensive troubleshooting is then carried out in accordance with the instructions provided in the diagnostic program or in the test instructions. Provided in the "Notes on the BMW DIAGNOSTIC SYSTEM" and "Troubleshooting" is detailed information on how and under what circumstances the relevant control unit detects a defect and its significance.
Important! On no account clear the defect codes before repair, otherwise important information (troubleshooting, additional information etc.) will no longer appear on the display screen.
Status Monitoring
With this function, it is possible to read out current statuses and values applied at the inputs and outputs of the control unit. This display must be compared with the actual status at the vehicle and its plausibility must be checked. If a signal is found to be defective or if the status detected by the control unit deviates from the actual status on the vehicle, troubleshooting must be carried out at the associated input or output. In the majority of cases, a defect can be localized by simple measurement (voltage, resistance, etc.).
Test Procedure
- Only in the diagnostic program of the BMW SERVICE TESTER -
This function makes it possible to perform a guided check of the system. The test procedure incorporates status monitoring, activation of components and, if necessary, also reading the defect code memory. The display screen pages contain detailed information texts on testing and troubleshooting.
Activating Components
With this function, components can be activated without the control unit internal switch-on conditions being set. The actual statuses at the input of the control unit are ignored. In this way, to locate defects, the function of components can be checked while they are still installed.
Special Functions
Special control unit functions can, in part, be called up via the diagnostic procedure (e.g.: system test, reading out coded data etc.).
Test Code
The test code must be printed out before renewing a control unit or an important component of the system. The printout is sent in together with the control unit or component.
The test code contains the coded defect code memory of the control unit. It facilitates fast analysis of the defective component by the Warranty and Quality Assurance departments.
Important! Print out test code before the defect code memory is cleared!
Clearing Defect Code Memory
The defect code memory must be cleared after all defects of the system have been rectified.
Service Tester Symbols
QUICK TEST
The quick test makes it possible to check all control units with self-diagnosis capabilities installed in the vehicle for stored defect codes.
The ignition must be switched on before starting the quick test (ignition switch in position 2!). The quick test is started from the overview of control units. "Quick Test Active" is masked in on the last line. The relevant line flashing shows the operator how far the quick test has progressed.
When the BMW DIAGNOSTIC SYSTEM detects a control unit, the corresponding line of the control unit overview is marked with a star.
When a defect code is stored in the defect code memory of a control unit, the line is displayed inversely (white highlighted) and marked with an "F".
On conclusion of the quick test, "Quick Test Completed" is masked in on the last line.
It is possible to terminate a currently running quick test at any time by pressing any key.
Quick Test in MoDiC
BMW MoDiC:
Start with the "down arrow" key in the overview of control units.
On conclusion of the quick test, an overview of control units appears which have been detected by the MoDiC diagnostic program. If a defect code is stored in a control unit, the corresponding line is highlighted in black.