Daewoo Nubira. Manual - part 124

ENGINE CONTROLS 1F – 407

DAEWOO V–121 BL4

A fault in the heated oxygen sensor (HO2S) heater ele-
ment or its ignition feed or ground will result in lower oxy-
gen sensor response. This may cause incorrect catalyst
monitor diagnostic results.

EXHAUST GAS RECIRCULATION
VALVE

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 powertrain control module (PCM)/engine control mod-
ule (ECM). The EGR valve feeds small amounts of ex-
haust gas into the intake manifold to decrease combustion
temperature. The amount of exhaust gas recirculated is
controlled by variations in vacuum and exhaust back pres-
sure. If too much exhaust gas enters, combustion will not
take place. For this reason, very little exhaust gas is al-
lowed to pass through the valve, especially at idle.

The EGR valve is usually open under the following condi-
tions:

Warm engine operation.

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:

The engine stops after a cold start.

The engine stops at idle after deceleration.

The vehicle surges during cruise.

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:

Spark knock (detonation)

Engine

overheating

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 powertrain control module (PCM)/engine control
module (ECM) provides 5 volts to the IAT sensor through
a resistor in the PCM/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
PCM/ECM knows the intake IAT by measuring the volt-
age.

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
powertrain control module (PCM)/engine control module
(ECM). The PCM/ECM sends voltage pulses to the IAC
valve motor windings, causing the IAC valve pintle tomove
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 PCM/ECM.
These programmed engine speeds are based on the cool-
ant temperature, the park/neutral position switch status,
the vehicle speed, the battery voltage, and the A/C system
pressure (if equipped).

The PCM/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 PCM/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 PCM/ECM can result in incorrect idle control or the
necessity to partially press the accelerator when starting
until the PCM/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.

1F – 408

ENGINE CONTROLS

DAEWOO V–121 BL4

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.

A closed throttle on engine coast down produces a rela-
tively low MAP output. MAP is the opposite of vacuum.
When manifold pressure is high, vacuum is low. The MAP
sensor is also used to measure barometric pressure. This
is performed as part of MAP sensor calculations. With the

ignition ON and the engine not running, the powertrain
control module (PCM)/engine control module (ECM) will
read the manifold pressure as barometric pressure and
adjust the air/fuel ratio accordingly. This compensation for
altitude allows the system to maintain driving performance
while holding emissions low. The barometric function will
update periodically during steady driving or under a wide
open throttle condition. In the case of a fault in the baro-
metric portion of the MAP sensor, the PCM/ECM will set
to the default value.

A failure in the MAP sensor circuit sets a diagnostic trouble
code P0107 or P0108.

The following tables show the difference between absolute pressure and vacuum related to MAP sensor output, which
appears as the top row of both tables.

MAP

Volts

4.9

4.4

3.8

3.3

2.7

2.2

1.7

1.1

0.6

0.3

kPa

100

in. Hg

29.6

26.6

23.7

20.7

17.7

14.8

11.8

8.9

5.9

2.9

VACUUM

Volts

4.9

4.4

3.8

3.3

2.7

2.2

1.7

1.1

0.6

0.3

kPa

100

in. Hg

2.9

5.9

8.9

11.8

14.8

17..7

20.7

23.7

26.7

29.6

POWERTRAIN CONTROL
MODULE/ENGINE CONTROL
MODULE

The powertrain control module (PCM)/engine control
module (ECM), located inside the passenger kick–panel,
is the control center of the fuel injection system. It
constantly looks at the information from various sensors
and controls the systems that affect the vehicle’s perfor-
mance. The PCM/ECM also performs the diagnostic func-
tions of the system. It can recognize operational problems,
alert the driver through the Malfunction Indicator Lamp
(MIL), and store diagnostic trouble code(s) which identify
problem areas to aid the technician in making repairs.

There are no serviceable parts in the PCM/ECM. The cal-
ibrations are stored in the PCM/ECM in the Programmable
Read–Only Memory (PROM).

The PCM/ECM supplies either 5 or 12 volts to power the
sensors or switches. This is done through resistances in
the PCM/ECM which are so high in value that a test light
will not come on when connected to the circuit. In some
cases, even an ordinary shop voltmeter will not give an ac-
curate reading because its resistance is too low. You must
use a digital voltmeter with a 10 megohm input impedance
to get accurate voltage readings. The PCM/ECM controls
output circuits such as the fuel injectors, the idle air control

valve, the A/C clutch relay, etc., by controlling the ground
circuit through transistors or a device called a ”quad–driv-
er.”

FUEL INJECTOR

The Multiport Fuel Injection (MFI) assembly is a solenoid–
operated device controlled by the powertrain control mod-
ule (PCM)/engine control module (ECM). It meters pres-
surized fuel to a single engine cylinder. The PCM/ECM
energizes the fuel injector or the solenoid to a normally
closed ball or pintle valve. This allows fuel to flow into the
top of the injector, past the ball or pintle valve, and through
a recessed flow director plate at the injector outlet.

The director plate has six machined holes that control the
fuel flow, generating a conical spray pattern of finely atom-
ized fuel at the injector tip. Fuel from the tip is directed at
the intake valve, causing it to become further atomized
and vaporized before entering the combustion chamber.
A fuel injector which is stuck partially open will cause a loss
of fuel pressure after the engine is shut down. Also, an ex-
tended crank time will be noticed on some engines. Diesel-
ing can also occur because some fuel can be delivered to
the engine after the ignition is turned OFF.

KNOCK SENSOR

The knock sensor detects abnormal knocking in the en-
gine. The sensor is mounted in the engine block near the
cylinders. The sensor produces an AC output voltage
which increases with the severity of the knock. This signal

ENGINE CONTROLS 1F – 409

DAEWOO V–121 BL4

is sent to the powertrain control module (PCM)/engine
control module (ECM). The PCM/ECM then adjusts the
ignition timing to reduce the spark knock.

G SENSOR

The powertrain control module (PCM)/engine control
module (ECM) receives rough road information from the
G sensor. The PCM/ECM uses the rough road information
to enable or disable the misfire diagnostic. The misfire
diagnostic can be greatly affected by crankshaft speed
variations caused by driving on rough road surfaces. The
G sensor generates rough road information by producing
a signal which is proportional to the movement of a small
metal bar inside the sensor.

If a fault occurs which causes the PCM/ECM to not receive
rough road information between 30 and 80 mph (50 and
132 km/h), DTC P1391 will set.

FUEL CUTOFF SWITCH

The fuel cutoff switch is a safety device. In the event of a
collision or sudden impact, it automatically cuts off the fuel
supply and activates the door lock relay. After the switch
has been activated, it must be reset in order to restart the
engine. To reset this fuel–cutoff feature, press the rubber
top of the switch located near the left side of the driver’s
seat.

STRATEGY–BASED DIAGNOSTICS

Strategy–Based Diagnostics

The strategy–based diagnostic is a uniform approach to
repair all Electrical/Electronic (E/E) systems. The diag-
nostic flow can always be used to resolve an E/E system
problem and is a starting point when repairs are neces-
sary. The following steps will instruct the technician on
how to proceed with a diagnosis:

Verify the customer complaint. To verify the cus-
tomer complaint, the technician should know the
normal operation of the system.

Perform preliminary checks as follows:

Conduct a thorough visual inspection.

Review the service history.

Detect unusual sounds or odors.

Gather Diagnostic Trouble Code (DTC) informa-

tion to achieve an effective repair.

Check bulletins and other service information. This
includes videos, newsletters, etc.

Refer to service information (manual) system
check(s).

Refer to service diagnostics.

No Trouble Found

This condition exists when the vehicle is found to operate
normally. The condition described by the customer may be
normal. Verify the customer complaint against another ve-

hicle that is operating normally. The condition may be in-
termittent. Verify the complaint under the conditions de-
scribed by the customer before releasing the vehicle.

Re–examine the complaint.

When the complaint cannot be successfully found or iso-
lated, a re–evaluation is necessary. The complaint should
be re–verified and could be intermittent as defined in ”In-
termittents,” or could be normal.

After isolating the cause, the repairs should be made. Vali-
date for proper operation and verify that the symptom has
been corrected. This may involve road testing or other
methods to verify that the complaint has been resolved un-
der the following conditions:

Conditions noted by the customer.

If a DTC was diagnosed, verify a repair by duplicat-
ing conditions present when the DTC was set as
noted in the Failure Records or Freeze Frame data.

Verifying Vehicle Repair

Verification of the vehicle repair will be more comprehen-
sive for vehicles with On–Board Diagnostic (OBD II) sys-
tem diagnostics. Following a repair, the technician should
perform these steps:

Important : Follow the steps below when you verify re-
pairs on OBD II systems. Failure to follow these steps
could result in unnecessary repairs.

Review and record the Failure Records and the
Freeze Frame data for the DTC which has been
diagnosed (Freeze Fame data will only be stored
for an A or B type diagnostic and only if the MIL
has been requested).

Clear the DTC(s).

Operate the vehicle within conditions noted in the
Failure Records and Freeze Frame data.

Monitor the DTC status information for the specific
DTC which has been diagnosed until the diagnostic
test associated with that DTC runs.

OBD II SERVICEABILITY ISSUES

Based on the knowledge gained from On–Board Diagnos-
tic (OBD II) experience in the 1994 and 1995 model years,
this list of non–vehicle faults that could affect the perfor-
mance of the OBD II system has been compiled. These
non–vehicle faults vary from environmental conditions to
the quality of fuel used. With the introduction of OBD II
diagnostics across the entire passenger car and light–duty
truck market in 1996, illumination of the MIL due to a non–
vehicle fault could lead to misdiagnosis of the vehicle, in-
creased warranty expense and customer dissatisfaction.
The following list of non–vehicle faults does not include ev-
ery possible fault and may not apply equally to all product
lines.

Fuel Quality

Fuel quality is not a new issue for the automotive industry,
but its potential for turning on the Malfunction Indicator
Lamp (MIL) with OBD II systems is new.

1F – 410

ENGINE CONTROLS

DAEWOO V–121 BL4

Fuel additives such as ”dry gas” and ”octane enhancers”
may affect the performance of the fuel. If this results in an
incomplete combustion or a partial burn, it will set DTC
P0300. The Reed Vapor Pressure of the fuel can also
create problems in the fuel system, especially during the
spring and fall months when severe ambient temperature
swings occur. A high Reed Vapor Pressure could show up
as a Fuel Trim DTC due to excessive canister loading.
High vapor pressures generated in the fuel tank can also
affect the Evaporative Emission diagnostic as well.

Using fuel with the wrong octane rating for your vehicle
may cause driveability problems. Many of the major fuel
companies advertise that using ”premium” gasoline will
improve the performance of your vehicle. Most premium
fuels use alcohol to increase the octane rating of the fuel.
Although alcohol–enhanced fuels may raise the octane
rating, the fuel’s ability to turn into vapor in cold tempera-
tures deteriorates. This may affect the starting ability and
cold driveability of the engine.

Low fuel levels can lead to fuel starvation, lean engine op-
eration, and eventually engine misfire.

Non–OEM Parts

All of the OBD II diagnostics have been calibrated to run
with Original Equipment Manufacturer (OEM) parts.
Something as simple as a high–performance exhaust sys-
tem that affects exhaust system back pressure could po-
tentially interfere with the operation of the Exhaust Gas
Recirculation (EGR) valve and thereby turn on the MIL.
Small leaks in the exhaust system near the post catalyst
oxygen sensor can also cause the MIL to turn on.

Aftermarket electronics, such as cellular phones, stereos,
and anti–theft devices, may radiate electromagnetic inter-
ference (EMI) into the control system if they are improperly
installed. This may cause a false sensor reading and turn
on the MIL.

Environment

Temporary environmental conditions, such as localized
flooding, will have an effect on the vehicle ignition system.
If the ignition system is rain–soaked, it can temporarily
cause engine misfire and turn on the MIL.

Refueling

A new OBD II diagnostic checks the integrity of the entire
Evaporative (EVAP) Emission system. If the vehicle is re-
started after refueling and the fuel cap is not secured cor-
rectly, the on–board diagnostic system will sense this as
a system fault, turn on the MIL, and set DTC P0440.

Vehicle Marshaling

The transportation of new vehicles from the assembly
plant to the dealership can involve as many as 60 key
cycles within 2 to 3 miles of driving. This type of operation
contributes to the fuel fouling of the spark plugs and will
turn on the MIL with a set DTC P0300.

Poor Vehicle Maintenance

The sensitivity of OBD II diagnostics will cause the MIL to
turn on if the vehicle is not maintained properly. Restricted
air filters, fuel filters, and crankcase deposits due to lack
of oil changes or improper oil viscosity can trigger actual
vehicle faults that were not previously monitored prior to
OBD II. Poor vehicle maintenance can not be classified as
a ”non–vehicle fault,” but with the sensitivity of OBD II
diagnostics, vehicle maintenance schedules must be
more closely followed.

Severe Vibration

The Misfire diagnostic measures small changes in the
rotational speed of the crankshaft. Severe driveline vibra-
tions in the vehicle, such as caused by an excessive
amount of mud on the wheels, can have the same effect
on crankshaft speed as misfire and, therefore, may set
DTC P0300.

Related System Faults

Many of the OBD II system diagnostics will not run if the
powertrain control module (PCM)/engine controlmodule
(ECM) detects a fault on a related system or component.
One example would be that if the PCM/ECM detected a
Misfire fault, the diagnostics on the catalytic converter
would be suspended until the Misfire fault was repaired. If
the Misfire fault is severe enough, the catalytic converter
can be damaged due to overheating and will never set a
Catalyst DTC until the Misfire fault is repaired and the Cat-
alyst diagnostic is allowed to run to completion. If this hap-
pens, the customer may have to make two trips to the
dealership in order to repair the vehicle.

SERIAL DATA COMMUNICATIONS

Class II Serial Data Communications

Government regulations require that all vehicle manufac-
turers establish a common communication system. This
vehicle utilizes the ”Class II” communication system. Each
bit of information can have one of two lengths: long or
short. This allows vehicle wiring to be reduced by transmit-
ting and receiving multiple signals over a single wire. The
messages carried on Class II data streams are also priori-
tized. If two messages attempt to establish communica-
tions on the data line at the same time, only the message
with higher priority will continue. The device with the lower
priority message must wait. Themost significant result of
this regulation is that it provides scan tool manufacturers
with the capability to access data from any make or model
vehicle that is sold.

The data displayed on the other scan tool will appear the
same, with some exceptions. Some scan tools will only be
able to display certain vehicle parameters as values that
are a coded representation of the true or actual value. On
this vehicle the scan tool displays the actual values for ve-
hicle parameters. It will not be necessary to perform any
conversions from coded values to actual values.

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