BMW 5251 Service Manual page 963

OBD-3
On-Board ~iactnosticsl
Additional MIL information:
A fault code is stored within the ECM upon the first
occurrence of a fault in the system being checlted.
Two complete consecutive drive cycles with the iault
present illuminate the MIL. The exception to the two-fault
requirement is a catalyst-damaging fault, which illuminates
the MIL immediately.
If the second drive cycle was not complete and the fault
was not checked, the ECM counts the third drive cycle as
the next consecutive drive cycle. The MIL illuminates if the
system is checked and the fault is still present.
Once the MIL is illuminated, it remains illuminated until the
vehicle completes three consecutive drive cycles without
detecting a fault.
0
An existing fault code is cleared from memory
automatically when the vehicle completes 40 consecutive
drive cycles without the fault being detected.
In order to automatically clear a catalyst-damaging fault from
memory, the condition underwhich the fault occurred must be
evaluated for 80 consecutive drive cycles without the fault
reoccurring.
A generic scan tool connected to the BMW data link
connector (DLC) or OBD I 1 plug can display diagnostic trouble
codes (DTCs), along with the conditions associated with the
illumination of the MIL. Using a more advanced or BMW-
dedicated scan tool, additional proprietary information is
normally available.
Scan tool and scan tool display
The complexity of the OBD I1 system requires that all
diagnostics begin by connecting a scan tool to the vehicle.
Aftermarltet scan tools can be connected to either the 16-pin
OBD I 1 plug or the 20-pin BMW DLC in the engine
compartment (ii installed). Data from the OBD II plug may be
limited, depending on scan tool and vehicle.
OBD I1 standards reouire that the 16-oin OBD I 1 oluo be
located within three (3) feet of the driier and not're&ire any
tools to access.
Starting with June 2000 production, the 20-pin BMW DLC,
previously located in the engine compartment, was
discontinued. Diagnostic, coding and programming functions
are incorporated into the OBD II plug, located under left side
of dashboard.
On cars built up to 06 / 2000: when accessing emissions
related DTCs through the 16-pin OBD I1 plug, malte sure the
BMW 20-oin DLC caD is installed.