BMW 1999-2005 M3 Service Manual page 1235

On-Board Diagnostics
8 of 11
http://ebahn.bentleypublishers.com/BMW/3/E46/Repair%20Manuals/8...
ECM cannot determine the
environment or engine operating
conditions due to missing or faulty
signals it will set a fault code and,
depending on conditions, illuminate the
MIL.
Oxygen sensor monitoring: When drive
conditions allow, response rate and
switching time of each oxygen sensor
is monitored. In addition, the heater
function is also monitored. The OBD II
"diagnostic executive" knows the
difference between upstream and
downstream oxygen sensors and reads
each one individually.
All oxygen sensors are monitored
separately. In order for the oxygen
sensor to be effectively monitored, the
system must be in closed loop
operation.
Catalyst monitoring: This strategy
monitors the two heated oxygen
sensors per bank of cylinders. It
compares the oxygen content going
into the catalytic converter to the
oxygen leaving the converter.
The diagnostic executive knows that
most of the oxygen should be used up
during the oxidation phase and if it
sees higher than programmed values,
a fault will be set and the MIL will
illuminate.
Misfire detection: This strategy
monitors crankshaft speed fluctuations
and determines if a misfire occurs by
variations in speed between each
crankshaft sensor trigger point. This
strategy is so finely tuned that it can
even determine the severity of the
misfire.
The diagnostic executive must
determine if misfire is occurring, as well
as other pertinent misfire information.
2/25/2009 11:22 PM