BMW 3 (E46). Manual - part 76
dimensional map similar to the one
shown is digitally stored in the ECM.
The initial ignition point is determined
by the crankshaft speed sensor during
cranking. Once the engine is running,
timing is continually adjusted based on
operating conditions.
Basic troubleshooting
principles
Poor driveability may have a variety of
causes. The fault may lie with the
ignition system, the fuel system, parts
of the emission control system, or a
combination of the three. Because of
these interrelated functions and their
effects on each other, it is often difficult
to know where to begin looking for
problems.
For this reason, effective
troubleshooting should always begin
with an interrogation of the On-Board
Diagnostics (OBD II) system. The OBD
II system detects engine management
malfunctions. When faults are
detected, the OBD II system stores a
Diagnostic Trouble Code (DTC) in the
Engine Control Module (ECM) along
with other pertinent fault information. In
addition, the Malfunction Indicator Light
(MIL) will come on if an emissions
related fault is detected. Additional
OBD II information, including a DTC
lookup table can be found in the back
of this manual under
OBD On Board
Diagnostics
.
Note:
On model year 1999 and 2000 cars, the
MIL is labeled Check Engine. On model
year 2001 cars, the MIL is labeled
Service Engine Soon.
An engine that starts and runs
indicates that the ignition system is