Daewoo Nubira. Manual - part 125

ENGINE CONTROLS 1F – 411

DAEWOO V–121 BL4

ON–BOARD DIAGNOSTIC (OBD II)

On–Board Diagnostic Tests

A diagnostic test is a series of steps, the result of which is
a pass or fail reported to the diagnostic executive. When
a diagnostic test reports a pass result, the diagnostic
executive records the following data:

The diagnostic test has been completed since the
last ignition cycle.

The diagnostic test has passed during the current
ignition cycle.

The fault identified by the diagnostic test is not cur-
rently active.

When a diagnostic test reports a fail result, the diagnostic
executive records the following data:

The diagnostic test has been completed since the
last ignition cycle.

The fault identified by the diagnostic test is current-
ly active.

The fault has been active during this ignition cycle.

The operating conditions at the time of the failure.

Remember, a fuel trim Diagnostic Trouble Code (DTC)
may be triggered by a list of vehicle faults. Make use of all
information available (other DTCs stored, rich or lean con-
dition, etc.) when diagnosing a fuel trim fault.

COMPREHENSIVE COMPONENT
MONITOR DIAGNOSTIC OPERATION

Comprehensive component monitoring diagnostics are
required to monitor emissions–related input and output
powertrain components.

Input Components

Input components are monitored for circuit continuity and
out–of–range values. This includes rationality checking.
Rationality checking refers to indicating a fault when the
signal from a sensor does not seem reasonable, i.e.
Throttle Position (TP) sensor that indicates high throttle
position at low engine loads or Manifold Absolute Pressure
(MAP) voltage. Input components may include, but are not
limited to, the following sensors:

Vehicle Speed Sensor (VSS).

Crankshaft Position (CKP) sensor.

Throttle Position (TP) sensor.

Engine Coolant Temperature (ECT) sensor.

Camshaft Position (CMP) sensor.

Manifold Absolute Pressure (MAP) sensor.

In addition to the circuit continuity and rationality check,
the ECT sensor is monitored for its ability to achieve a
steady state temperature to enable closed loop fuel con-
trol.

Output Components

Output components are diagnosed for proper response to
control module commands. Components where functional
monitoring is not feasible will be monitored for circuit conti-
nuity and out–of–range values if applicable. Output com-
ponents to be monitored include, but are not limited to the
following circuit:

Idle Air Control (IAC) Motor.

Control module controlled EVAP Canister Purge
Valve.

A/C

relays.

Cooling fan relay.

VSS

output.

MIL

control.

Cruise control inhibit.

Refer to ”Powertrain Control Module/Engine Control Mod-
ule” and Sensors in this section.

Passive and Active Diagnostic Tests

A passive test is a diagnostic test which simply monitors
a vehicle system or component. Conversely, an active
test, actually takes some sort of action when performing
diagnostic functions, often in response to a failed passive
test. For example, the Exhaust Gas Recirculation (EGR)
diagnostic active test will force the EGR valve open during
closed throttle deceleration and/or force the EGR valve
closed during a steady state. Either action should result in
a change in manifold pressure.

Intrusive Diagnostic Tests

This is any on–board test run by the Diagnostic Manage-
ment System which may have an effect on vehicle perfor-
mance or emission levels.

Warm–Up Cycle

A warm–up cycle means that engine temperature must
reach aminimum of 160

F (70

C) and rise at least 72

(22

C) over the course of a trip.

Freeze Frame

Freeze Frame is an element of the Diagnostic Manage-
ment System which stores various vehicle information at
the moment an emissions–related fault is stored in
memory and when the Malfunction Indicator Lamp (MIL)
is commanded on. These data can help to identify the
cause of a fault.

Failure Records

Failure Records data is an enhancement of the OBD II
Freeze Frame feature. Failure Records store the same ve-
hicle information as does Freeze Frame, but it will store
that information for any fault which is stored in onboard
memory, while Freeze Frame stores information only for
emission–related faults that command the MIL on.

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COMMON OBD II TERMS

Diagnostic

When used as a noun, the word diagnostic refers to any
on–board test run by the vehicle

’

s Diagnostic Manage-

ment System. A diagnostic is simply a test run on a system
or component to determine if the system or component is
operating according to specification. There are many diag-
nostics, shown in the following list:

Misfire

Oxygen Sensors (O2S)

Heated Oxygen Sensor (HO2S)

Exhaust Gas Recirculation (EGR)

Catalyst

monitoring

Enable Criteria

The term ”enable criteria” is engineering language for the
conditions necessary for a given diagnostic test to run.
Each diagnostic has a specific list of conditions which
must be met before the diagnostic will run.

”Enable criteria” is another way of saying ”conditions re-
quired.”

The enable criteria for each diagnostic is listed on the first
page of the Diagnostic Trouble Code (DTC) description
under the heading ”Conditions for Setting the DTC.” En-
able criteria varies with each diagnostic and typically in-
cludes, but is not limited to, the following items:

Engine

speed.

Vehicle

speed

Engine Coolant Temperature (ECT)

Manifold Absolute Pressure (MAP)

Barometric Pressure (BARO)

Intake Air Temperature (IAT)

Throttle Position (TP)

High canister purge

Fuel

trim

A/C

Trip

Technically, a trip is a key–on run key–off cycle in which all
the enable criteria for a given diagnostic are met, allowing
the diagnostic to run. Unfortunately, this concept is not
quite that simple. A trip is official when all the enable crite-
ria for a given diagnostic are met. But because the enable
criteria vary from one diagnostic to another, the definition
of trip varies as well. Some diagnostics are run when the
vehicle is at operating temperature, some when the ve-
hicle first starts up; some require that the vehicle be cruis-
ing at a steady highway speed, some run only when the
vehicle is at idle; some diagnostics function with the
Torque Converter Clutch (TCC) disabled. Some run only
immediately following a cold engine startup.

A trip then, is defined as a key–on run key–off cycle in
which the vehicle was operated in such a way as to satisfy
the enables criteria for a given diagnostic, and this diag-
nostic will consider this cycle to be one trip. However,

another diagnostic with a different set of enable criteria
(which were not met) during this driving event, would not
consider it a trip. No trip will occur for that particular diag-
nostic until the vehicle is driven in such a way as to meet
all the enable criteria

Diagnostic Information

The diagnostic charts and functional checks are designed
to locate a faulty circuit or component through a process
of logical decisions. The charts are prepared with the re-
quirement that the vehicle functioned correctly at the time
of assembly and that there are not multiple faults present.

There is a continuous self–diagnosis on certain control
functions. This diagnostic capability is complimented by
the diagnostic procedures contained in this manual. The
language of communicating the source of the malfunction
is a system of diagnostic trouble codes. When a malfunc-
tion is detected by the control module, a diagnostic trouble
code is set and the Malfunction Indicator Lamp (MIL) is illu-
minated.

Malfunction Indicator Lamp (MIL)

The Malfunction Indicator Lamp (MIL) is required by On–
Board Diagnostics (OBD II) that it illuminates under a strict
set of guide lines.

Basically, the MIL is turned on when the powertrain control
module (PCM)/engine control module (ECM) detects a
DTC that will impact the vehicle emissions.

The MIL is under the control of the Diagnostic Executive.
The MIL will be turned on if an emissions–related diagnos-
tic test indicates a malfunction has occurred. It will stay on
until the system or component passes the same test, for
three consecutive trips, with no emissions related faults.

Extinguishing the MIL

When the MIL is on, the Diagnostic Executive will turn off
the MIL after three consecutive trips that a ”test passed”
has been reported for the diagnostic test that originally
caused the MIL to illuminate. Although the MIL has been
turned off, the DTC will remain in the PCM/ECM memory
(both Freeze Frame and Failure Records) until forty (40)
warm–up cycles after no faults have been completed.

If the MIL was set by either a fuel trim or misfire–related
DTC, additional requirements must be met. In addition to
the requirements stated in the previous paragraph, these
requirements are as follows:

The diagnostic tests that are passed must occur
with 375 rpm of the rpm data stored at the time the
last test failed.

Plus or minus ten percent of the engine load that
was stored at the time the last test failed. Similar
engine temperature conditions (warmed up or
warming up) as those stored at the time the last
test failed.

Meeting these requirements ensures that the fault which
turned on the MIL has been corrected.

The MIL is on the instrument panel and has the following
functions:

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DAEWOO V–121 BL4

It informs the driver that a fault that affects vehicle
emission levels has occurred and that the vehicle
should be taken for service as soon as possible.

As a system check, the MIL will come on with the
key ON and the engine not running. When the en-
gine is started, the MIL will turn OFF.

When the MIL remains ON while the engine is run-
ning, or when a malfunction is suspected due to a
driveability or emissions problem, an OBD II Sys-
tem Check must be performed. The procedures for
these checks are given in OBD II System Check.
These checks will expose faults which may not be
detected if other diagnostics are performed first.

Data Link Connector (DLC)

The provision for communicating with the control module
is the Data Link Connector (DLC). The DLC is used to con-
nect to a scan tool. Some common uses of the scan tool
are listed below:

Identifying stored DTCs.

Clearing

DTCs.

Performing output control tests.

Reading serial data.

DTC TYPES

Each Diagnostic Trouble Code (DTC) is directly related to
a diagnostic test. The Diagnostic Management System
sets DTC based on the failure of the tests during a trip or
trips. Certain tests must fail two consecutive trips before
the DTC is set. The following are the three types of DTCs
and the characteristics of those codes:

Type A

Emissions

related.

Requests illumination of the Malfunction Indicator
Lamp (MIL) of the first trip with a fail.

Stores a History DTC on the first trip with a fail.

Stores a Freeze Frame (if empty).

Stores a Fail Record.

Updates the Fail Record each time the diagnostic
test fails.

Type B

Emissions

related.

”Armed” after one trip with a fail.

”Disarmed” after one trip with a pass.

Requests illumination of the MIL on the second
consecutive trip with a fail.

Stores a History DTC on the second consecutive
trip with a fail (The DTC will be armed after the first
fail).

Stores a Freeze Frame on the second consecutive
trip with a fail (if empty).

Store Fail Record when the first test fails (not de-
pendent on consecutive trip fails).

Updates the Fail Record each time the diagnostic
test fails.

Type D

(Type D non–emissions related are not utilized on certain
vehicle applications).

Non–Emissions

related.

Does not request illumination of any lamp.

Stores a History DTC on the first trip with a fail.

Does not store a Freeze Frame.

Stores Fail Record when test fails.

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 Executive
has the capability of alerting the vehicle operator to poten-
tially damaging levels of misfire. If a misfire condition ex-
ists that could potentially damage the catalytic converter
as a result of high misfire levels, the Diagnostic 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 diagnos-
tics. Each time a fuel trim or misfire malfunction is de-
tected, engine load, engine speed, and engine coolant
temperature (ECT) are recorded.

When the ignition is turned off, the last reported set of con-
ditions 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 nor-
mal Type B diagnostic, and does not use the stored condi-
tions. However, if a malfunction occurs on two non–con-
secutive trips, the stored conditions are compared with the
current conditions. The MIL will then illuminate under the
following conditions:

When the engine load conditions are within 10% of
the previous test that failed.

Engine speed is within 375 rpm of the previous test
that failed.

ECT is in the same range as the previous test that
failed.

READING DIAGNOSTIC TROUBLE
CODES

The procedure for reading diagnostic trouble code(s) is to
use a diagnostic scan tool. When reading Diagnostic
Trouble Codes (DTCs), follow the instructions supplied by
tool manufacturer.

Clearing Diagnostic Trouble Codes

Important : Do not clear DTCs unless directed to do so
by the service information provided for each diagnostic
procedure. When DTCs are cleared, the Freeze Frame

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DAEWOO V–121 BL4

and Failure Record data which may help diagnose an in-
termittent fault will also be erased from memory. If the fault
that caused the DTC to be stored into memory has been
corrected, the Diagnostic Executive will begin to count the
”warm–up” cycles with no further faults detected, the DTC
will automatically be cleared from the powertrain control
module (PCM)/engine control module (ECM) memory.

To clear DTCs, use the diagnostic scan tool. When a scan
tool is not available, DTCs can also be cleared by discon-
necting one of the following sources for at least thirty (30)
seconds:

Notice : To prevent system damage, the ignition key must
be OFF when disconnecting or reconnecting battery pow-
er.

The power source to the control module. Examples:
fuse, pigtail at battery PCM/ECM connectors etc.

The negative battery cable. (Disconnecting the neg-
ative battery cable will result in the loss of other
onboard memory data, such as preset radio tun-
ing).

DTC Modes

On On–Board Diagnostic (OBD II) passenger cars there
are five options available in the scan tool DTC mode to dis-
play the enhanced information available. A description of
the new modes, DTC Info and Specific DTC, follows. After
selecting DTC, the following menu appears:

DTC

Info.

Specific

DTC.

Freeze

Frame.

Fail Records (not all applications).

Clear

Info.

The following is a brief description of each of the sub me-
nus in DTC Info and Specific DTC. The order in which they
appear here is alphabetical and not necessarily the way
they will appear on the scan tool.

DTC Information Mode

Use the DTC info mode to search for a specific type of
stored DTC information. There are seven choices. The
service manual may instruct the technician to test for
DTCs in a certain manner. Always follow published service
procedures.

To get a complete description of any status, press the ”En-
ter” key before pressing the desired F–key. For example,
pressing ”Enter” then an F–key will display a definition of
the abbreviated scan tool status.

DTC Status

This selection will display any DTCs that have not run dur-
ing the current ignition cycle or have reported a test failure
during this ignition up to a maximum of 33 DTCs. DTC
tests which run and pass will cause that DTC number to
be removed from the scan tool screen.

Fail This Ign. (Fail This Ignition)

This selection will display all DTCs that have failed during
the present ignition cycle.

History

This selection will display only DTCs that are stored in the
PCM/ECM’s history memory. It will not display type B
DTCs that have not requested the Malfunction Indicator
Lamp (MIL). It will display all type A and B DTCs that have
requested the MIL and have failed within the last 40 warm–
up cycles. In addition, it will display all type C and type D
DTCs that have failed within the last 40 warm–up cycles.

Last Test Fail

This selection will display only DTCs that failed the last
time the test ran. The last test may have run during a pre-
vious ignition cycle if a type A or type B DTC is displayed.
For type C and type D DTCs, the last failure must have oc-
curred during the current ignition cycle to appear as Last
Test Fail.

MIL Request

This selection will display only DTCs that are requesting
the MIL. Type C and type D DTCs cannot be displayed us-
ing this option. This selection will report type B DTCs only
after the MIL has been requested.

Not Run SCC (Not Run Since Code Clear)

This option will display up to 33 DTCs that have not run
since the DTCs were last cleared. Since any displayed
DTCs have not run, their condition (passing or failing) is
unknown.

Test Fail SCC (Test Failed Since Code
Clear)

This selection will display all active and history DTCs that
have reported a test failure since the last time DTCs were
cleared. DTCs that last failed more than 40 warm–up
cycles before this option is selected will not be displayed.

Specific DTC Mode

This mode is used to check the status of individual diag-
nostic tests by DTC number. This selection can be ac-
cessed if a DTC has passed, failed or both. Many OBD II
DTC mode descriptions are possible because of the ex-
tensive amount of information that the diagnostic execu-
tive monitors regarding each test. Some of the many pos-
sible descriptions follow with a brief explanation.

The ”F2” key is used, in this mode, to display a description
of the DTC. The ”Yes” and ”No” keys may also be used to
display more DTC status information. This selection will
only allow entry of DTC numbers that are supported by the
vehicle being tested. If an attempt is made to enter DTC
numbers for tests which the diagnostic executive does not
recognize, the requested information will not be displayed
correctly and the scan tool may display an error message.
The same applies to using the DTC trigger option in the
Snapshot mode. If an invalid DTC is entered, the scan tool
will not trigger.

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