Diagnostic Trouble Codes With Test Charts: Introduction

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES , proceed with self-diagnostics. BMW vehicles are equipped with 2 separate self-diagnostic systems. OBD-II self-diagnostic system accesses Diagnostic Trouble Codes (DLCs) using a generic scan tool connected to vehicle Data Link Connector (DLC). See Fig 1-Fig 3 . BMW self-diagnostic system accesses DTCs using special BMW hardware and software connected to BMW engine diagnostic connector socket. See Fig 4.

Regardless of self-diagnostic system, DME/Motronic 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. See 1997 MODEL COVERAGE  table. These substitute values are canceled when normal engine operation is resumed.

Fig 1: Locating OBD-II Data Link Connector (Z3)

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Locating OBD-II Data Link Connector (3, 5 & 8-Series)

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 3: Locating OBD-II Data Link Connector (7-Series)

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 4: Locating BMW Engine Diagnostic Connector Socket (4-Cylinder Engine Shown; Others Are Similar)

Courtesy of BMW OF NORTH AMERICA, INC.

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 TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).