Diagnostic Trouble Codes With Test Charts: Introduction: Notes

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES , proceed with self-diagnostics. OBD-II Diagnostic Trouble Codes (DTCs) are accessed using a generic scan tool connected to vehicle Data Link Connector (DLC). See Fig 1. BMW trouble codes can be accessed using BMW's GROUP TESTER ONE (GT-1) or DISplus hardware system.

Beginning with model year 2001, the E39, E46 and E53 eliminated the 20-pin BMW diagnostic connector from the engine compartment. The 16-pin OBD-II connector located inside vehicle is the only diagnosis port. The E38 and Z3 will continue to use the 20-pin connector until the end of production. The 16-pin OBD-II connector has been in all BMWs since 1996 to comply with OBD-II regulations requiring a standardized diagnostic port. Before 2001, only emissions relevant data could be extracted from OBD-II connector because it did not provide access to the TXD (D-bus). The TXD line is connected to pin No. 8 of the OBD-II connector on vehicles without the 20-pin diagnostic connector. The OBD-II connector is located in driver's footwell to left of steering column for E39, E46 and E53 vehicles.

On 7-series vehicles, diagnosis tool is connected to the vehicle at the OBD-II diagnosis connector (On-Board Diagnosis). The connector is located behind a small cover in the drivers side lower "A" pillar trim. There is a black plastic cap that bridges KL30 to the D-bus when the connector is not being used. This cap must be removed before installing the diagnosis cable. The TXD lead is located in pin 7 of the OBD socket and is connected directly to the ZGM. The ZGM detects by means of the data transmission speed whether a BMW diagnosis tool (DISplus, GT-1) or an aftermarket scanner is connected. The PCM allows access to different data depending on diagnosis tool connected. When using an OBD-II scan tool for diagnosis, the transmission speed is 10.4 KBit/s. See Fig 2.

The Motronic/Siemens control unit provides a substitute value if a failure occurs in an engine performance related component, such as engine (coolant) temperature sensor, intake air temperature sensor, airflow meter or exhaust gas oxygen sensor. These substitute values are canceled when normal engine operation is resumed.

If no DTCs are present after entering self-diagnostics, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). For engine management system identification, see ENGINE MANAGEMENT SYSTEM IDENTIFICATION (2002)  table.

Fig 1: Locating OBD-II Connector

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Diagnosis Using OBD-II Connector

Courtesy of BMW OF NORTH AMERICA, INC.