2004 DAEWOO LACETTI engine coolant

1F – 604IENGINE CONTROLS
DAEWOO V–121 BL4
4. Disconnect the coolant hose from the throttle body.
5. Disconnect the throttle cables by opening the re-
lease slot.
6. Disconnect the main throttle idle actuator (MTIA)
electrical connector.
7. Remove the throttle body bolt and the nuts.
8. Remove the throttle body.
Installation Procedure
1. Install the throttle body assembly to the intake man-
ifold.
2. Install the throttle body retaining nuts and the bolt.
Tighten
Tighten the throttle body retaining nuts and the bolt to
15 NSm (11 lb–ft).
3. Connect the throttle cable.
4. Connect the coolant hoses.
5. Connect the breather hose.
6. Install the intake air tube.
7. Connect the negative battery cable.
THROTTLE BODY (1.8L DOHC)
Removal Procedure
1. Disconnect the negative battery cable.
2. Disconnect the intake air temperature (IAT) sensor
connector.
3. Disconnect the breather hose from the valve cover.
4. Remove the air intake tube.

ENGINE CONTROLS 1F – 605
DAEWOO V–121 BL4
5. Disconnect the throttle cables by opening the
throttle and moving the cable through the release
slot.
6. Disconnect the vacuum hoses from the throttle
body.
7. Disconnect the throttle position (TP) sensor and the
idle air control valve connectors.
8. Disconnect the coolant hoses from the throttle
body.
9. Remove the throttle body retaining nuts.
Notice : Cover the opening of the intake manifold after re-
moving the throttle body assembly. This will prevent any
objects or debris from entering the engine which may
cause damage.
10. Remove the throttle body and discard the gasket.
11. Remove the TP sensor. Refer to ”Throttle Position
Sensor ”in this section.
12. Remove the idle air control (IAC) valve. Refer to
”Idle Air Control Valve ”in this section.
Installation Procedure
Notice : Use care in cleaning old gasket material from ma-
chined aluminum surfaces. Sharp tools may damage seal-
ing surfaces.
1. Clean the gasket mating surface on the intake man-
ifold.
Notice : The throttle body may be cleaned in a cold immer-
sion–type cleaner following disassembly. The TP sensor
and the idle air control valve should not come in contact
with any solvent or cleaner, as they may be damaged.
2. Clean the throttle body.
3. Install the TP sensor. Refer to ” Throttle Position
Sensor ”in this section.
4. Install the IAC valve. Refer to ”Idle Air Control Valve
” in this section.
5. Install the throttle body assembly with a new gasket
to the intake manifold.
6. Install the throttle body retaining nuts.
Tighten
Tighten the throttle body retaining nuts to 10 NSm (89
lb–in).

1F – 606IENGINE CONTROLS
DAEWOO V–121 BL4
7. Connect the TP sensor connector and the IAC
valve connector.
8. Connect the coolant hoses to the throttle body.
9. Connect the vacuum hoses to the throttle body.
Important : Make sure the throttle/cruise control cables
do not hold the throttle open. With the engine off, check to
see that the accelerator pedal is free.
10. Connect the throttle cable.
11. Install the air intake tube.
12. Connect the breather hose to the valve cover.
13. Connect the IAT sensor connector.
14. Connect the negative battery cable.
15. Fill the cooling system.
FRONT HEATED OXYGEN SENSOR
(HO2S1) (1.4L/1.6L DOHC)
Removal Procedure
1. Disconnect the negative battery cable.
Notice : The oxygen sensor uses a permanently attached
pigtail and connector. This pigtail should not be removed
from the oxygen sensor. Damage or removal of the pigtail
or the connector could affect proper operation of the oxy-
gen sensor. Take care when handling the oxygen sensor.
Do not drop the oxygen sensor.
2. Disconnect the front heated oxygen sensor
(HO2S1) connector.
Notice : The oxygen sensor may be difficult to remove
when engine temperature is below 48°C (120°F). Exces-
sive force may damage threads in the exhaust manifold.
3. Carefully remove the HO2S1 from the exhaust
manifold.
Installation Procedure
Important : A special anti–seize compound is used on the
oxygen sensor threads. This compound consists of a liq-
uid graphite and glass beads. The graphite will burn away,
but the glass beads will remain, making the sensor easier
to remove. New or service sensors will already have the
compound applied to the threads. If a sensor is removed
from any engine and if for any reason it is to be reinstalled,
the threads must have anti–seize compound applied be-
fore reinstallation.
1. Coat the threads of the HO2S1 with an anti–seize
compound, if needed.
2. Install the HO2S1 into the exhaust manifold.
Tighten
Tighten the oxygen sensor to 42 NSm (31 lb–ft).
3. Connect the HO2S1 connector.
4. Connect the negative battery cable.

ENGINE CONTROLS 1F – 623
DAEWOO V–121 BL4
GENERAL DESCRIPTION
AND SYSTEM OPERATION
IGNITION SYSTEM OPERATION
This ignition system does not use a conventional distribu-
tor and coil. It uses a crankshaft position sensor input to
the engine control module (ECM). The ECM then deter-
mines Electronic Spark Timing (EST) and triggers the di-
rect ignition system ignition coil.
This type of distributorless ignition system uses a ”waste
spark” method of spark distribution. Each cylinder is
paired with the cylinder that is opposite it (1–4 or 2–3). The
spark occurs simultaneously in the cylinder coming up on
the compression stroke and in the cylinder coming up on
the exhaust stroke. The cylinder on the exhaust stroke re-
quires very little of the available energy to fire the spark
plug. The remaining energy is available to the spark plug
in the cylinder on the compression stroke.
These systems use the EST signal from the ECM to con-
trol the electronic spark timing. The ECM uses the follow-
ing information:
S Engine load (manifold pressure or vacuum).
S Atmospheric (barometric) pressure.
S Engine temperature.
S Intake air temperature.
S Crankshaft position.
S Engine speed (rpm).
ELECTRONIC IGNITION SYSTEM
IGNITION COIL
The Electronic Ignition (EI) system ignition coil provides
the spark for two spark plugs simultaneously. The EI sys-
tem ignition coil is not serviceable and must be replaced
as an assembly.
CRANKSHAFT POSITION SENSOR
This direct ignition system uses a magnetic crankshaft
position sensor. This sensor protrudes through its mount
to within approximately 0.05 inch (1.3 mm) of the crank-
shaft reluctor. The reluctor is a special wheel attached to
the crankshaft or crankshaft pulley with 58 slots machined
into it, 57 of which are equally spaced in 6 degree intervals.
The last slot is wider and serves to generate a ”sync
pulse.” As the crankshaft rotates, the slots in the reluctor
change the magnetic field of the sensor, creating an in-
duced voltage pulse. The longer pulse of the 58th slot
identifies a specific orientation of the crankshaft and al-
lows the engine control module (ECM) to determine the
crankshaft orientation at all times. The ECM uses this in-
formation to generate timed ignition and injection pulses
that it sends to the ignition coils and to the fuel injectors.
CAMAHAFT POSITION SENSOR
The Camshaft Position (CMP) sensor sends a CMP sen-
sor signal to the engine control module (ECM). The ECM
uses this signal as a ”sync pulse” to trigger the injectors in
the proper sequence. The ECM uses the CMP sensor sig-
nal to indicate the position of the #1 piston during its power
stroke. This allows the ECM to calculate true sequential
fuel injection mode of operation. If the ECM detects an in-
correct CMP sensor signal while the engine is running,
DTC P0341 will set. If the CMP sensor signal is lost while
the engine is running, the fuel injection system will shift to
a calculated sequential fuel injection mode based on the
last fuel injection pulse, and the engine will continue to run.
As long as the fault is present, the engine can be restarted.
It will run in the calculated sequential mode with a 1–in–6
chance of the injector sequence being correct.
IDLE AIR SYSTEM OPERATION
The idle air system operation is controlled by the base idle
setting of the throttle body and the Idle Air Control (IAC)
valve.
The engine control module (ECM) uses the IAC valve to
set the idle speed dependent on conditions. The ECM
uses information from various inputs, such as coolant tem-
perature, manifold vacuum, etc., for the effective control
of the idle speed.
FUEL CONTROL SYSTEM
OPERATION
The function of the fuel metering system is to deliver the
correct amount of fuel to the engine under all operating
conditions. The fuel is delivered to the engine by the indi-
vidual fuel injectors mounted into the intake manifold near
each cylinder.
The two main fuel control sensors are the Manifold Abso-
lute Pressure (MAP) sensor, the Front Heated Oxygen
Sensor (HO2S1) and the Rear Heated Oxygen Sensor
(HO2S2).
The MAP sensor measures or senses the intake manifold
vacuum. Under high fuel demands the MAP sensor reads
a low vacuum condition, such as wide open throttle. The
engine control module (ECM) uses this information to ri-
chen the mixture, thus increasing the fuel injector on–time,
to provide the correct amount of fuel. When decelerating,
the vacuum increases. This vacuum change is sensed by
the MAP sensor and read by the ECM, which then de-
creases the fuel injector on–time due to the low fuel de-
mand conditions.
HO2S Sensors
The HO2S sensor is located in the exhaust manifold. The
HO2S sensor indicates to the ECM the amount of oxygen
in the exhaust gas and the ECM changes the air/fuel ratio
to the engine by controlling the fuel injectors. The best air/
fuel ratio to minimize exhaust emissions is 14.7 to 1, which
allows the catalytic converter to operate most efficiently.

1F – 624IENGINE CONTROLS
DAEWOO V–121 BL4
Because of the constant measuring and adjusting of the
air/fuel ratio, the fuel injection system is called a ”closed
loop” system.
The ECM uses voltage inputs from several sensors to de-
termine how much fuel to provide to the engine. The fuel
is delivered under one of several conditions, called
”modes.”
Starting Mode
When the ignition is turned ON, the ECM turns the fuel
pump relay on for two seconds. The fuel pump then builds
fuel pressure. The ECM also checks the Engine Coolant
Temperature (ECT) sensor and the Throttle Position (TP)
sensor and determines the proper air/fuel ratio for starting
the engine. This ranges from 1.5 to 1 at –97 °F (–36 °C)
coolant temperature to 14.7 to 1 at 201 °F (94 °C) coolant
temperature. The ECM controls the amount of fuel deliv-
ered in the starting mode by changing how long the fuel in-
jector is turned on and off. This is done by ”pulsing” the fuel
injectors for very short times.
Clear Flood Mode
If the engine floods with excessive fuel, it may be cleared
by pushing the accelerator pedal down all the way. The
ECM will then completely turn off the fuel by eliminating
any fuel injector signal. The ECM holds this injector rate
as long as the throttle stays wide open and the engine is
below approximately 400. If the throttle position becomes
less than approximately 80 percent, the ECM returns to
the starting mode.
Run Mode
The run mode has two conditions called ”open loop” and
”closed loop.”
Open Loop
When the engine is first started and it is above 400 rpm,
the system goes into ”open loop” operation. In ”open loop,”
the ECM ignores the signal from the HO2S and calculates
the air/fuel ratio based on inputs from the ECT sensor and
the MAP sensor. The sensor stays in ”open loop” until the
following conditions are met:
S The HO2S sensor has a varying voltage output,
showing that it is hot enough to operate properly.
S The ECT sensor is above a specified temperature.
S A specific amount of time has elapsed after starting
the engine.
Closed Loop
The specific values for the above conditions vary with dif-
ferent engines and are stored in the Electronically Eras-
able Programmable Read–Only Memory (EEPROM).
When these conditions are met, the system goes into
”closed loop” operation. In ”closed loop,” the ECM calcu-
lates the air/fuel ratio (fuel injector on–time) based on the
signal from the oxygen sensor. This allows the air/fuel ratio
to stay very close to 14.7 to 1.Acceleration Mode
The ECM responds to rapid changes in throttle position
and airflow and provides extra fuel.
Deceleration Mode
The ECM responds to changes in throttle position and air-
flow and reduces the amount of fuel. When deceleration
is very fast, the ECM can cut off fuel completely for short
periods of time.
Battery Voltage Correction Mode
When battery voltage is low, the ECM can compensate for
a weak spark delivered by the ignition module by using the
following methods:
S Increasing the fuel injector pulse width.
S Increasing the idle speed rpm.
S Increasing the ignition dwell time.
Fuel Cut–Off Mode
No fuel is delivered by the fuel injectors when the ignition
is OFF. This prevents dieseling or engine run–on. Also, the
fuel is not delivered if there are no reference pulses re-
ceived from the central power supply. This prevents flood-
ing.
EVAPORATIVE EMISSION CONTROL
SYSTEM OPERATION
The basic Evaporative (EVAP) Emission control system
used is the charcoal canister storage method. This meth-
od transfers fuel vapor from the fuel tank to an activated
carbon (charcoal) storage device (canister) to hold the va-
pors when the vehicle is not operating. When the engine
is running, the fuel vapor is purged from the carbon ele-
ment by intake airflow and consumed in the normal com-
bustion process.
Gasoline vapors from the fuel tank flow into the tube la-
beled TANK. These vapors are absorbed into the carbon.
The canister is purged by the engine control module
(ECM) when the engine has been running for a specified
amount of time. Air is drawn into the canister and mixed
with the vapor. This mixture is then drawn into the intake
manifold.
The ECM supplies a ground to energize the EVAP emis-
sion canister purge solenoid valve. This valve is Pulse
Width Modulated (PWM) or turned on and off several
times a second. The EVAP emission canister purge PWM
duty cycle varies according to operating conditions deter-
mined by mass airflow, fuel trim, and intake air tempera-
ture.
Poor idle, stalling, and poor driveability can be caused by
the following conditions:
S An inoperative EVAP emission canister purge sole-
noid valve.
S A damaged canister.
S Hoses that are split, cracked, or not connected to
the proper tubes.

ENGINE CONTROLS 1F – 625
DAEWOO V–121 BL4
EVAPORATIVE EMISSION CANISTER
The Evaporative (EVAP) Emission canister is an emission
control device containing activated charcoal granules.
The EVAP emission canister is used to store fuel vapors
from the fuel tank. Once certain conditions are met, the en-
gine control module (ECM) activates the EVAP canister
purge solenoid, allowing the fuel vapors to be drawn into
the engine cylinders and burned.
POSITIVE CRANKCASE
VENTILATION SYSTEM OPERATION
A Positive Crankcase Ventilation (PCV) system is used to
provide complete use of the crankcase vapors. Fresh air
from the air cleaner is supplied to the crankcase. The fresh
air is mixed with blowby gases which are then passed
through a vacuum hose into the intake manifold.
Periodically inspect the hoses and the clamps. Replace
any crankcase ventilation components as required.
A restricted or plugged PCV hose may cause the following
conditions:
S Rough idle
S Stalling or low idle speed
S Oil leaks
S Oil in the air cleaner
S Sludge in the engine
A leaking PCV hose may cause the following conditions:
S Rough idle
S Stalling
S High idle speed
ENGINE COOLANT TEMPERATURE
SENSOR
The Engine Coolant Temperature (ECT) sensor is a
thermistor (a resistor which changes value based on tem-
perature) mounted in the engine coolant stream. Low cool-
ant temperature produces a high resistance (100,000
ohms at –40 °F [–40 °C]) while high temperature causes
low resistance (70 ohms at 266 °F [130 °C]).
The engine control module (ECM) supplies 5 volts to the
ECT sensor through a resistor in the ECM and measures
the change in voltage. The voltage will be high when the
engine is cold, and low when the engine is hot. By measur-
ing the change in voltage, the ECM can determine the
coolant temperature. The engine coolant temperature af-
fects most of the systems that the ECM controls. A failure
in the ECT sensor circuit should set a diagnostic trouble
code P0117 or P0118. Remember, these diagnostic
trouble codes indicate a failure in the ECT sensor circuit,
so proper use of the chart will lead either to repairing a wir-
ing problem or to replacing the sensor to repair a problem
properly.
THROTTLE POSITION SENSOR
The Throttle Position (TP) sensor is a potentiometer con-
nected to the throttle shaft of the throttle body. The TP sen-
sor electrical circuit consists of a 5 volt supply line and a
ground line, both provided by the engine control module
(ECM). The ECM calculates the throttle position by moni-
toring the voltage on this signal line. The TP sensor output
changes as the accelerator pedal is moved, changing the
throttle valve angle. At a closed throttle position, the output
of the TP sensor is low, about 0.5 volt. As the throttle valve
opens, the output increases so that, at Wide Open Throttle
(WOT), the output voltage will be about 5 volts.
The ECM can determine fuel delivery based on throttle
valve angle (driver demand). A broken or loose TP sensor
can cause intermittent bursts of fuel from the injector and
an unstable idle, because the ECM thinks the throttle is
moving. A problem in any of the TP sensor circuits should
set a diagnostic trouble code (DTC) P0121 or P0122.
Once the DTC is set, the ECM will substitute a default val-
ue for the TP sensor and some vehicle performance will
return. A DTC P0121 will cause a high idle speed.
CATALYST MONITOR OXYGEN
SENSORS
Three–way catalytic converters are used to control emis-
sions of hydrocarbons (HC), carbon monoxide (CO), and
oxides of nitrogen (NOx). The catalyst within the convert-
ers promotes a chemical reaction. This reaction oxidizes
the HC and CO present in the exhaust gas and converts
them into harmless water vapor and carbon dioxide. The
catalyst also reduces NOx by converting it to nitrogen. The
engine control module (ECM) can monitor this process us-
ing the HO2S1 and HO2S2 sensor. These sensors pro-
duce an output signal which indicates the amount of oxy-
gen present in the exhaust gas entering and leaving the
three–way converter. This indicates the catalyst’s ability to
efficiently convert exhaust gasses. If the catalyst is operat-
ing efficiently, the HO2S1 sensor signals will be more ac-
tive than the signals produced by the HO2S2 sensor. The
catalyst monitor sensors operate the same way as the fuel
control sensors. The sensor’s main function is catalyst
monitoring, but they also have a limited role in fuel control.
If a sensor output indicates a voltage either above or below
the 450 mv bias voltage for an extended period of time, the
ECM will make a slight adjustment to fuel trim to ensure
that fuel delivery is correct for catalyst monitoring.
A problem with the HO2S1 sensor circuit will set DTC
P0131, P0132, P0133 or P0134 depending, on the special
condition. A problem with the HO2S2 sensor signal will set
DTC P0137, P0138, P0140 or P0141, depending on the
special condition.
A fault in the Rear Heated Oxygen Sensor (HO2S2) heat-
er element or its ignition feed or ground will result in lower
oxygen sensor response. This may cause incorrect cata-
lyst monitor diagnostic results.

1F – 626IENGINE CONTROLS
DAEWOO V–121 BL4
EXHAUST GAS RECIRCULATION
VA LV E
The Exhaust Gas Recirculation (EGR) system is used on
engines equipped with an automatic transaxle to lower
NOx (oxides of nitrogen) emission levels caused by high
combustion temperature. The EGR valve is controlled by
the engine control module (ECM). The EGR valve feeds
small amounts of exhaust gas into the intake manifold to
decrease combustion temperature. The amount of ex-
haust gas recirculated is controlled by variations in vacu-
um and exhaust back pressure. If too much exhaust gas
enters, combustion will not take place. For this reason,
very little exhaust gas is allowed to pass through the valve,
especially at idle.
The EGR valve is usually open under the following condi-
tions:
S Warm engine operation.
S Above idle speed.
Results of Incorrect Operation
Too much EGR flow tends to weaken combustion, causing
the engine to run roughly or to stop. With too much EGR
flow at idle, cruise, or cold operation, any of the following
conditions may occur:
S The engine stops after a cold start.
S The engine stops at idle after deceleration.
S The vehicle surges during cruise.
S Rough idle.
If the EGR valve stays open all the time, the engine may
not idle. Too little or no EGR flow allows combustion tem-
peratures to get too high during acceleration and load con-
ditions. This could cause the following conditions:
S Spark knock (detonation)
S Engine overheating
S Emission test failure
INTAKE AIR TEMPERATURE
SENSOR
The Intake Air Temperature (IAT) sensor is a thermistor,
a resistor which changes value based on the temperature
of the air entering the engine. Low temperature produces
a high resistance (4,500 ohms at –40°F [–40°C]), while
high temperature causes a low resistance (70 ohms at
266°F [130°C]).
The engine control module (ECM) provides 5 volts to the
IAT sensor through a resistor in the ECM and measures
the change in voltage to determine the IAT. The voltage will
be high when the manifold air is cold and low when the air
is hot. The ECM knows the intake IAT by measuring the
voltage.
The IAT sensor is also used to control spark timing when
the manifold air is cold.
A failure in the IAT sensor circuit sets a diagnostic trouble
code P0112 or P0113.
IDLE AIR CONTROL VALVE
Notice : Do not attempt to remove the protective cap to
readjust the stop screw. Misadjustment may result in dam-
age to the Idle Air Control (IAC) valve or to the throttle
body.
The IAC valve is mounted on the throttle body where it
controls the engine idle speed under the command of the
engine control module (ECM). The ECM sends voltage
pulses to the IAC valve motor windings, causing the IAC
valve pintle to move in or out a given distance (a step or
count) for each pulse. The pintle movement controls the
airflow around the throttle valves which, in turn, control the
engine idle speed.
The desired idle speeds for all engine operating conditions
are programmed into the calibration of the ECM. These
programmed engine speeds are based on the coolant
temperature, the park/neutral position switch status, the
vehicle speed, the battery voltage, and the A/C system
pressure (if equipped).
The ECM ”learns” the proper IAC valve positions to
achieve warm, stabilized idle speeds (rpm) desired for the
various conditions (park/neutral or drive, A/C on or off, if
equipped). This information is stored in ECM ”keep alive”
memories. Information is retained after the ignition is
turned OFF. All other IAC valve positioning is calculated
based on these memory values. As a result, engine varia-
tions due to wear and variations in the minimum throttle
valve position (within limits) do not affect engine idle
speeds. This system provides correct idle control under all
conditions. This also means that disconnecting power to
the ECM can result in incorrect idle control or the necessity
to partially press the accelerator when starting until the
ECM relearns idle control.
Engine idle speed is a function of total airflow into the en-
gine based on the IAC valve pintle position, the throttle
valve opening, and the calibrated vacuum loss through ac-
cessories. The minimum throttle valve position is set at the
factory with a stop screw. This setting allows enough air-
flow by the throttle valve to cause the IAC valve pintle to
be positioned a calibrated number of steps (counts) from
the seat during ”controlled” idle operation. The minimum
throttle valve position setting on this engine should not be
considered the ”minimum idle speed,” as on other fuel in-
jected engines. The throttle stop screw is covered with a
plug at the factory following adjustment.
If the IAC valve is suspected as the cause of improper idle
speed, refer to ”Idle Air Control System Check” in this sec-
tion.
MANIFOLD ABSOLUTE PRESSURE
SENSOR
The Manifold Absolute Pressure (MAP) sensor measures
the changes in the intake manifold pressure which result
from engine load and speed changes. It converts these to
a voltage output.

1F – 630IENGINE CONTROLS
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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:
S Vehicle Speed Sensor (VSS).
S Crankshaft Position (CKP) sensor.
S Throttle Position (TP) sensor.
S Engine Coolant Temperature (ECT) sensor.
S Camshaft Position (CMP) sensor.
S 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:
S Idle Air Control (IAC) Motor.
S Control module controlled EVAP Canister Purge
Valve.
S A/C relays.
S Cooling fan relay.
S VSS output.
S MIL control.
Refer to ”Engine Control Module” and Sensors in this sec-
tion.
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°F
(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 EOBD
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.
COMMON EOBD 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:
S Misfire
S Front Heated Oxygen Sensor (HO2S1)
S Rear Heated Oxygen Sensor (HO2S2)
S Exhaust Gas Recirculation (EGR)
S 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:
S Engine speed.
S Vehicle speed
S Engine Coolant Temperature (ECT)
S Manifold Absolute Pressure (MAP)