Electronic Engine Controls
DIAGNOSIS AND TESTING
detected in either the STFT or LTFT, and it is still
present on a second trip, the MIL will be switched
on.
Heated Oxygen Sensor (H02S) Monitor (All except
vehicles with diesel engine)
This monitors the operation of the pre (upstream)
and post (downstream) catalytic converter
H02S
sensors. It will detect deviations in airlfuel ratios
(AFR) and sensor faults.
The
H02S will cause emission increase when its
response time increases too much. To diagnose
a sensor a period is measured and the number of
leanlrich transitions are counted. The sum of valid
periods is then calculated. To avoid
non-representative measurements, the period is
valid only if the
H02S has been below a low
threshold and above a high threshold between 2
consecutive leanlrich transitions.
A failure is
declared when the sum of the measured periods
exceeds the sum of the corresponding limit (held
within the PCM) and the MIL is illuminated.
Catalytic Converter Efficiency Monitor (All except
vehicles with diesel engine)
The efficiency of a catalytic converter is measured
by its ability to store and later release oxygen to
convert harmful gases. The efficiency is reduced
if the converter becomes contaminated as it ages,
and at high gas flow rates, because the exhaust
gas does not remain in the converter long enough
to complete the conversion process. switches
over or until the end of a delay. If this
delay expires or the sensor does not switch, the
sensor is treated as failed.
Combustion Noise Monitor (Vehicles with common
rail fuel injection)
In diesel variants, the Combustion Noise Monitor
is used to trim the fuel injection pulse lengths. Each
fuel injector has an associated set of correction
data that is determined during a production end of
line test. The Combustion Noise Monitor is used
to determine how the fuel injector characteristic
changes from this initial calibration over the life of
the fuel injector.
EGR Monitor (Vehicles with diesel engine)
The functionality of the EGR system is checked by
comparing either the MAP sensor output or EGR
valve lift potentiometer output (depending upon
application) with expected values.
Diagnostic Requirements
Vehicles equipped with EOBD, can be diagnosed
using the WDS. In order for the EOBD system to
be invoked, a number of criteria must be met. After
any repair, which could affect emissions, a trip must
be carried out on the vehicle, to make sure that
engine management system operates correctly.
Malfunction Indicator Lamp (MIL)
The MIL is located in the instrument cluster and is
fitted to alert the driver to the fact that an abnormal
This monitor checks for the oxygen storage condition
has developed in the engine management
capacity (OSC) of the catalytic converter. During system,
that is having an adverse effect on
a controlled period, the catalyst monitor sensor emissions.
In cases of misfires which are likely to
signal is analyzed to evaluate the OSC of the cause
catalytic converter damage, it is switched
catalyst. It represents the quantity of oxygen that on immediately.
With all other faults it will illuminate
is really used for the oxidation-reduction reaction continuously
from the second trip after the condition
by the catalytic converter If a fault has occurred occurred.
Under normal operation it should
with the catalyst monitor sensor during the catalyst illuminate
at key-on and go out almost as soon as
diagnosis, a sensor diagnosis is carried out. During the
engine is started.
the controlled diagnosis phase, the catalyst monitor
Diagnostic Trouble Codes (DTCs) sensor activity is measured and is compared to the
OSC of the catalyst. If this activity is high (low The
DTCs given
by the PCM are standardized,
0SC)theMILwillbeilluminated.Ifthroughoutthe whichmeansthatgenericscantoolscanread
controlled phase, repeated several times, the results from
all vehicles.
downstream sensor output has not moved, the
closed loop mode is delayed in order to test the
sensor. If the catalyst monitor sensor is set to rich,
the injection time is forced to lean and conversely
if the downstream sensor is set to lean, the
injection time is forced to rich until the sensor
2006.0 Fiesta 1212006 G384566en
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