Daewoo CIELO EURO III, Manual

Page: 590 / 603

1F – 4 2 0 ENGINE CONTROLS
DAEWOO T-154 BL2,3
D
Stores a History DTC on the first trip with a fail .
D
Does not store a Freeze Frame.
D
Stores Fail Record when test fails.
D
Updates the Fail Record each time the diagnostic test
fails.
Important: Only four Fail Records can be stored. Each
Fail Record is for a different DTC. It is possible that there
will not be Fail Records for every DTC if multiple DTCs
are set.
Special Cases of Type B Diagnostic Tests
Unique to the misfire diagnostic, the Diagnostic Execu-
tive has the capability of alerting the vehicle operator to
potentially damaging levels of misfire. If a misfire condi-
tion exists that could potentially damage the catalytic
converter as a result of high misfire levels, the Diagnos-
tic Executive will command the MIL to “flash” at a rate of
once per second during those the time that the catalyst
damaging misfire condition is present.
Fuel trim and misfire are special cases of Type B diag-
nostics. Each time a fuel trim or misfire malfunction is
detected, engine load, engine speed, and Engine Cool-
ant Temperature (ECT) are recorded.
When the ignition is turned off, the last reported set of
conditions remain stored. During subsequent ignition
cycles, the stored conditions are used as a reference for
similar conditions. If a malfunction occurs during two
consecutive trips, the Diagnostic Executive treats the
failure as a normal Type B diagnostic, and does not use
the stored conditions. However, if a malfunction occurs
on two non–consecutive trips, the stored conditions are
compared with the current conditions. The MIL will then
illuminate under the following conditions:
D
When the engine load conditions are within 10% of
the previous test that failed.
D
Engine speed is within 375 rpm, of the previous test
that failed.
D
ECT is in the same range as the previous test that
failed.
PRIMARY SYSTEM-BASED
DIAGNOSTICS
There are primary system-based diagnostics which
evaluate system operation and its effect on vehicle
emissions. The primary system–based diagnostics are
listed below with a brief description of the diagnostic
function:
Oxygen Sensor Diagnosis
The fuel control Oxygen Sensor (O2S 1) is diagnosed
for the following conditions:
D
Slow response
D
Response time (time to switch R/L or L/R)
D
Inactive signal (output steady at bias voltage approx.
450 mv)
D
Signal fixed high
D
Signal fixed low
The catalyst monitor Heated Oxygen Sensor (HO2S 2)
is diagnosed for the following conditions:
D
Heater performance (time to activity on cold start).
D
Signal fixed low during steady state conditions or
power enrichment (hard acceleration when a rich mix-
ture should be indicated).
D
Signal fixed high during steady state conditions or de-
celeration mode (deceleration when a lean mixture
should be indicated).
D
Inactive sensor (output steady at approx. 438 mv).
If the oxygen sensor pigtail wiring, connector or terminal
are damaged, the entire oxygen sensor assembly must
be replaced. Do not attempt to repair the wiring, connec-
tor or terminals. In order for the sensor to function prop-
erly, it must have clean reference air provided to it. This
clean air reference is obtained by way of the oxygen
sensor wire(s). Any attempt to repair the wires, connec-
tor or terminals could result in the obstruction of the ref-
erence air and degrade oxygen sensor performance.
Misfire Monitor Diagnostic Operation
The misfire monitor diagnostic is based on crankshaft
rotational velocity (reference period) variations. The
engine control module
(ECM) determines crankshaft rotational velocity using
the Crankshaft Position (CKP) sensor and the Camshaft
Position (CMP) sensor. When a cylinder misfires, the
crankshaft slows down momentarily. By monitoring the
CKP and CMP sensor signals, the ECM can calcu-
late when a misfire occurs.
For a non-catalyst damaging misfire, the diagnostic will
be required to monitor a misfire present for between
1000-3200 engine revolutions.
For catalyst-damaging misfire, the diagnostic will re-
spond to misfire within 200 engine revolutions.
Rough roads may cause false misfire detection. A rough
road will cause torque to be applied to the drive wheels
and drive train. This torque can intermittently decrease
the crankshaft rotational velocity. This may be falsely
detected as a misfire.
A rough road sensor, or “G sensor,” works together with
the misfire detection system. The G sensor produces a
voltage that varies along with the intensity of road vibra-
tions. When the ECM detects a rough road, the
misfire detection system is temporarily disabled.
Misfire Counters
Whenever a cylinder misfires, the misfire diagnostic
counts the misfire and notes the crankshaft position at
the time the misfire occurred. These “misfire counters”
are basically a file on each engine cylinder. A current
and a history misfire counter are maintained for each
cylinder. The misfire current counters (Misfire Cur #1-4)
indicate the number of firing events out of the last
200 cylinder firing events which were misfires. The mis-
fire current counter will display real time data without a