spark DAEWOO MATIZ 2003 Service User Guide

1E–4 ENGINE ELECTRICAL
DAEWOO M-150 BL2
3. In both vehicles, apply the parking brake firmly.
Notice: Make sure the cables are not on or near pulleys,
fans, or other parts that will move when the engine
starts, damaging the parts.
4. Shift a manual transaxle to NEUTRAL.
Caution: Do not use cables that have loose or miss-
ing insulation, or injury could result.
5. Clamp one end of the first jumper cable to the positive
terminal on the battery. Make sure it does not touch
any other metal parts. Clamp the other end of the
same cable to the positive terminal on the other bat-
tery. Never connect the other end to the negative ter-
minal of the discharged battery.
Caution: Do not attach the cable directly to the neg-
ative terminal of the discharged battery. Doing so
could cause sparks and possible battery explosion.
6. Clamp one end of the second cable to the negative
terminal of the booster battery. Make the final con-
nection to a solid engine ground, such as the engine
lift bracket, at least 450 millimeters (18 inches) from
the discharged battery.
7. Start the engine of the vehicle with the good battery.
Run the engine at a moderate speed for several min-
utes. Then start the engine of the vehicle which has
the discharged battery.
8. Remove the jumper cables by reversing the above
sequence exactly. Remove the negative cable from
the vehicle with the discharged battery first. While re-
moving each clamp, take care that it does not touch
any other metal while the other end remains at-
tached
.
GENERATOR
The Delco-Remy CS charging system has several mod-
els available, including the ∅114D (A-type) or CS114D
(B-type). The number denotes the outer diameter in
millimeters of the stator lamination.
CS generators are equipped with internal regulators.
The Y connection (A-type) or Delta (B-type) stator, a
rectifier bridge, and a rotor with slip rings and brushes
are electrically similar to earlier generators. A conven-
tional pulley and fan are used. There is no test hole.
Unlike three-wire generators, the ∅114D (A-type) or
CS114D (B-type) may be used with only two connec-
tions: battery positive and an ‘‘L’’ terminal to the charge
indicator lamp.
As with other charging systems, the charge indicator
lamp lights when the ignition switch is turned to ON, and
goes out when the engine is running. If the charge indi-
cator is on with the engine running, a charging system
defect is indicated.
The regulator voltage setting varies with temperature
and limits the system voltage by controlling the rotorfield current. The regulator switches rotor field current
on and off. By varying the on-off time, correct average
field current for proper system voltage control is ob-
tained. At high speeds, the on-time may be 10 percent
and the off-time 90 percent. At low speeds, with high
electrical loads, on-time may be 90 percent and the off-
time 10 percent.
CHARGING SYSTEM
The Delco-Remy CS charging system has several mod-
els available, including the ∅114D (A-type) or CS114D
(B-type). The number denotes the outer diameter in
millimeters of the stator laminations.
CS generators use a new type of regulator that incorpo-
rates a diode trio. The Y connection (A-type) or Delta (B-
type) stator, a rectifier bridge, and a rotor with slip rings
and brushes are electrically similar to earlier generators.
A conventional pulley and fan are used. There is no test
hole.
STARTER
Wound field starter motors have pole pieces, arranged
around the armature, which are energized by wound
field coils.
Enclosed shift lever cranking motors have the shift lever
mechanism and the solenoid plunger enclosed in the
drive housing, protecting them from exposure to dirt, icy
conditions, and splashes.
In the basic circuit, solenoid windings are energized
when the switch is closed. The resulting plunger and
shift lever movement causes the pinion to engage the
engine flywheel ring gear. The solenoid main contacts
close. Cranking then takes place.
When the engine starts, pinion overrun protects the ar-
mature from excessive speed until the switch is opened,
at which time the return spring causes the pinion to dis-
engage. To prevent excessive overrun, the switch
should be released immediately after the engine starts.
STARTING SYSTEM
The engine electrical system includes the battery, the
ignition, the starter, the generator, and all the related wir-
ing. Diagnostic tables will aid in troubleshooting system
faults. When a fault is traced to a particular component,
refer to that component section of the service manual.
The starting system circuit consists of the battery, the
starter motor, the ignition switch, and all the related elec-
trical wiring. All of these components are connected
electrically
.
DISTRIBUTOR
Distributor distributes the high tension voltage induced
from ignition coil, to each spark plug of each cylinder in

ENGINE ELECTRICAL 1E–5
DAEWOO M-150 BL2
the sequence of ignition order. It also adjusts the ignition
timing according to the engine condition.
This vehicle uses the distributor (optical sensor type)
which controls the preminary current of the ignition coil
by the ECM.
The ignition timing change is controlled electronically by
the ECM.
When diagnosing the ignition system, refer to Section
1F, Engine Controls.
IGNITION COIL
Ignition coil is a sort of transformer to generate high volt-
age (15,000–25,000V) which can bring spark at the
spark plugs and has an iron cored closed magnetic type.The closed magnetic typed ignition coil is used for the
High Energy Ignition (H.E.I) system. Comparing with the
iron cored open magnetic type, the closed type almost
has no loss of magnetic flux, and smaller in size, so it
produces the high voltage of secondary voltage.
SPARK PLUG
It is a part of ignition secondary current, and it burns the
compressed mixture by sparking the high voltage in-
duced from the ignition coil.

ENGINE ELECTRICAL 1E–9
DAEWOO M-150 BL2
IGNITION SYSTEM
D102E404
1 Ignition Coil
2 Spark Pulg
3 Ignitoin Wire (#0)
4 Ignition Wires (#1, #2, #3)
5 Support Clamp
6 Mounting Clamp
7 Distributor Assembly
8 Coupling
9 Distributor Oil Seal
10 Distributor Housing
11 Distributor Shaft12 Plate
13 Optical Sensor Unit
14 Plate
15 Bushing
16 Disc Wheel
17 Inner Cover
18 Outer Cover
19 Distributor Rotor
20 Distributor Cap Seal
21 Distributor Cap

ENGINE ELECTRICAL 1E–11
DAEWOO M-150 BL2
IGNITION SYSTEM (Cont’d)
ConditionProbable CauseCorrection
Hard to Starting the Engine
Faulty ignition coil.
Replace the ignition coil.

Faulty distributor (include the
optical sensor).
Replace the distributor or the
optical sensor.

Faulty spark plug.
Replace the spark plug or Adjust
the gap.

Poor ignition timing.
Reset the valve timing.
Engine Idling State is Unstable
Faulty spark plug.
Replace the spark plug or Adjust
the gap.

Faulty ignition coil.
Replace the ignition coil.

Poor ignition timing.
Reset the valve timing.
Poor Engine Accelerating
Poor ignition timing.
Reset the valve timing.

ENGINE ELECTRICAL 1E–41
DAEWOO M-150 BL2
SPECIFICATIONS
STARTER SPECIFICATIONS
ApplicationDescriptionUnitStandardLimit
Starter MotorType–SD 80–
Output(Capacity)kW0.8–
No Load Test @ 9 volts
Drive Pinion SpeedA
RPM150
2,000–
Brushes Lengthmm (in.)11.3–11.5
(0.445–0.453)7.0–7.25
(0.275–0.285)
GENERATOR SPECIFICATIONS
ApplicationDescriptionUnitStandardLimit
GeneratorTypeA-Type–J114D(MANDO)–GeneratorTypeA-Type
B-Type–J114D(MANDO)
CS114D(DAC)–
RegulatorA-TypeV14.4–15.0–Regulator
VoltageA-Type
B-TypeV14.4–15.0
14.3–4.9–
Brushes
LengthA-Type
B-Typemm (in.)18.5 (0.728)
20.0 (0.787)13.5 (0.531)
14 (0.551)
OutputA-Type–12V, 65A–Output
(Capacity)A-Type
B-Type–12V, 65A
12V, 65A–
IGNITION SYSTEM SPECIFICATIONS
ApplicationDescriptionUnitStandardLimit
Ignition CoilType–Closed
Magnetic Type–
First Coil ResistanceΩ1.2
10%–
Second Coil ResistanceKΩ12.1
15%–
DistributorType–Optical Sensor
Type–
Spark PlugTypeUnlead–BPR5EY-11–
RN9YC4–
WR8DCX–
TypeLead–BPR5EY–
RN9YC–
WR8DC–
Spark PlugGapUnleadmm (in.)1.1 (0.043)–
1.2 (0.047)–
Leadmm (in.)0.8 (0.031)–
Ignition WireIgnition Wire ResistanceKΩ/m2.5–12.0–

1E–42 ENGINE ELECTRICAL
DAEWOO M-150 BL2
BATTERY SPECIFICATIONS
ApplicationDescriptionUnitStandardLimit
BatteryType–MF–
CapacityAH35–
Cold Cranking AmpsCCA246–
FASTENER TIGHTENING SPECIFICATIONS
ApplicationNmLb-FtLb-In
Distributor Bolts10–16–89–142
Battery Retainer Clamp–to–Battery Rod Nuts6–8–53–71
Battery Carrier Tray Bolts9–12–80–106
Battery Cable Nuts9–12–80–106
Starter field Connector Nut9–12–80–106
Starter Through–Bolts4–6–35–53
Starter Mounting Bolts55–6541–48–
Starter Solenoid Assembly Screws6–8–53–71
Starter Solenoid Nuts9–12–80–106
Spark Plug20–3015–22–
Generator Through–Bolts4–6–35–53
Generator Drive End Nut80–11 059–81–
Generator Battery Lead Connector Nut4–7–35–62
Generator Bearing Plate Bolt6–8–53–71
Generator Brush Holder / Rectifier Screw9–12–80–106
Generator Belt Tension Adjusting Bolt18–2813–21–
Generator Shackle Bracket Bolt45–5533–41–
Generator Lower Bracket–to–Generator Bolt/Nut18–2813–21–
Ground Bolt35–4126–30–
Ignition Coil Screw4–7–35–62
Ignition Coil Bracket Bolt9–12–80–106

ENGINE CONTROLS 1F–3
DAEWOO M-150 BL2
DTC P1628 Immobilizer No Successful
Communication 1F-270. . . . . . . . . . . . . . . . . . . . . . .
DTC P1629 Immovilizer Wrong Computation 1F-272
DTC P0656 Fuel Level Gauge Circuit Fault 1F-274.
DTC P1660 Malfunction Indicator Lamp (MIL)
High Voltage 1F-276. . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P1661 Malfunction Indicator Lamp (MIL)
Low Voltage 1F-278. . . . . . . . . . . . . . . . . . . . . . . . . .
Symptom Diagnosis 1F-280. . . . . . . . . . . . . . . . . . . . . .
Important Preliminary Checks 1F-280. . . . . . . . . . . . .
Intermittent 1F-281. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hard Start 1F-283. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Surges or Chuggles 1F-286. . . . . . . . . . . . . . . . . . . . .
Lack of Power, Sluggishness or Sponginess 1F-288
Detonation/Spark Knock 1F-290. . . . . . . . . . . . . . . . . .
Hesitation, Sag, Stumble 1F-292. . . . . . . . . . . . . . . . .
Cuts Out, Misses 1F-294. . . . . . . . . . . . . . . . . . . . . . . .
Poor Fuel Economy 1F-296. . . . . . . . . . . . . . . . . . . . . .
Rough, Unstable, or Incorrect Idle, Stalling 1F-297. .
Excessive Exhaust Emissions or Odors 1F-300. . . .
Dieseling, Run-on 1F-302. . . . . . . . . . . . . . . . . . . . . . .
Backfire 1F-303. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Maintenance and Repair 1F-304. . . . . . . . . . . . . . . . . .
On-Vehicle Service 1F–304 . . . . . . . . . . . . . . . . . . . . . . .
Fuel Pump 1F–304 . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuel Pressure Regulator 1F-305. . . . . . . . . . . . . . . . .
Fuel Filter 1F-306. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuel Tank 1F-307. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuel Rail and Injectors 1F-308. . . . . . . . . . . . . . . . . . .
Evaporator Emission Canister 1F-309. . . . . . . . . . . . . Evaporator Emission Canister Purge
Solenoid 1F-310. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Manifold Absolute Pressure (MAP) Sensor 1F-310. .
Throttle Body 1F-311. . . . . . . . . . . . . . . . . . . . . . . . . . .
Engine Coolant Temperature (ECT) Sensor 1F-312.
Intake Air Temperature (ECT) Sensor 1F-313. . . . . .
Oxygen Sensor (O2S 1) 1F-314. . . . . . . . . . . . . . . . . .
Heated Oxygen Sensor (HO2S 2) 1F-314. . . . . . . . .
Electric Exhaust Gas Recirculation (EEGR)
Valve 1F-315. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Knock Sensor 1F-315. . . . . . . . . . . . . . . . . . . . . . . . . . .
Electronic Ignition (EI) System Ignition Coil 1F-316.
Crankshaft Position (CKP) Sensor 1F-316. . . . . . . .
Camshaft Position (CMP) Sensor 1F-317. . . . . . . . . .
Engine Control Module (ECM) 1F-317. . . . . . . . . . . . .
Specifications 1F-319. . . . . . . . . . . . . . . . . . . . . . . . . . .
Fastener Tightening Specification 1F-319. . . . . . . . . .
Special Tools 1F-319. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Special Tools Table 1F-319. . . . . . . . . . . . . . . . . . . . . .
Schematic and Routing Diagrams 1F-320. . . . . . . . .
ECM Wiring Diagram
(Sirius D3 – 1 of 5) 1F-320. . . . . . . . . . . . . . . . . . . .
ECM Wiring Diagram
(Sirius D3 – 2 of 5) 1F-321. . . . . . . . . . . . . . . . . . . .
ECM Wiring Diagram
(Sirius D3 – 3 of 5) 1F-322. . . . . . . . . . . . . . . . . . . .
ECM Wiring Diagram
(Sirius D3 – 4 of 5) 1F-323. . . . . . . . . . . . . . . . . . . .
ECM Wiring Diagram
(Sirius D3 – 5 of 5) 1F-324. . . . . . . . . . . . . . . . . . . .

1F–4 ENGINE CONTROLS
DAEWOO M-150 BL2
DESCRIPTION AND OPERATION
IGNITION SYSTEM OPERATION
This ignition system does not use a conventional distrib-
utor and coil. It uses a crankshaft position sensor input
to the Engine Control Module (ECM). The ECM then de-
termines Electronic Spark Timing (EST) and triggers the
electronic ignition system ignition coil.
This type of distributorless ignition system uses a “waste
spark’’ method of spark distribution. Each cylinder is in-
dividural with coil per cylinder.
These systems use the EST signal from the ECM to
control the EST. The ECM uses the following informa-
tion:

Engine load (manifold pressure or vacuum).

Atmospheric (barometric) pressure.

Engine temperature.

Intake air temperature.

Crankshaft position.

Engine speed (rpm).
ELECTRONIC IGNITION SYSTEM
IGNITION COIL
The Electronic Ignition (EI) system ignition coil is
mounted near on the cylinder head.
A terminals of the EI system ignition coil provides the
spark for each spark plug. The EI system ignition coil is
not serviceable and must be replaced as an assembly.
CRANKSHAFT POSITION SENSOR
This Electronic Ignition (EI) system uses a magnetic
crankshaft position sensor. This sensor protrudes
through its mount to within approximately 1.3 mm (0.05
inch) of the crankshaft reluctor. The reluctor is a special
wheel attached to the crankshaft with 58 slots machined
into it, 57 of which are equally spaced in 6-degree inter-
vals. 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, creat-
ing an induced voltage pulse. The longer pulse of the
58th slot identifies a specific orientation of the crank-
shaft and allows the Engine Control Module (ECM) to
determine the crankshaft orientation at all times. The
ECM uses this information to generate timed ignition
and injection pulses that it sends to the ignition coils and
to the fuel injectors.
CAMSHAFT POSITION SENSOR
The Camshaft Position (CMP) sensor sends a CMP sig-
nal 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 signal to indi-
cate the position of the #1 piston during its power stroke.
This allows the ECM to calculate true sequential fuel in-jection mode of operation. If the ECM detects an incor-
rect CMP signal while the engine is running, Diagnostic
Trouble Code (DTC) P0341 will set. If the CMP 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 en-
gine can be restarted. It will run in the calculated se-
quential 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
temperature, 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 in-
dividual fuel injectors mounted into the intake manifold
near each cylinder.
The main fuel control sensors are the Manifold Absolute
Pressure (MAP) sensor, the oxygen sensor (O2S), and
the heated oxygen sensor (HO2S).
The MAP sensor measures or senses the intake man-
ifold 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 in-
formation to enrich 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 decreases the fuel injector on-time
due to the low fuel demand conditions.
The O2S is located in the exhaust manifold. The HO2S
is located in the exhaust pipe. The oxygen sensors indi-
cate to the ECM the amount of oxygen in the exhaust
gas, and the ECM changes the air/fuel ratio to the en-
gine by controlling the fuel injectors. The best air/fuel ra-
tio to minimize exhaust emissions is 14.7:1, which
allows the catalytic converter to operate most efficiently.
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
determine how much fuel to provide to the engine. The

ENGINE CONTROLS 1F–5
DAEWOO M-150 BL2
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 2 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. The ECM controls the amount of
fuel delivered in the starting mode by changing how long
the fuel injector is turned on and off. This is done by
“pulsing’’ the fuel injectors for very short times.
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 O2S and cal-
culates the air/fuel ratio based on inputs from the ECT
sensor and the MAP sensor. The ECM stays in ”open
loop” until the following conditions are met:

The O2S has a varying voltage output, showing that it
is hot enough to operate properly.

The ECT sensor is above a specified temperature.

A specific amount of time has elapsed after starting
the engine.
Closed Loop
The specific values for the above conditions vary with
different engines and are stored in the Electronically
Erasable Programmable Read-Only Memory (EE-
PROM). When these conditions are met, the system
goes into “closed loop” operation. In “closed loop,” the
ECM calculates the air/fuel ratio (fuel injector on-time)
based on the signals from the oxygen sensors. This al-
lows 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
airflow and reduces the amount of fuel. When decelera-
tion 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 us-
ing the following methods:

Increasing the fuel injector pulse width.

Increasing the idle speed rpm.

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 CKP sensor. This prevents flooding.
EVAPORATIVE EMISSION CONTROL
SYSTEM OPERATION
The basic Evaporative Emission (EVAP) control system
used is the charcoal canister storage method. This
method transfers fuel vapor from the fuel tank to an acti-
vated carbon (charcoal) storage canister which holds
the vapors when the vehicle is not operating. When the
engine is running, the fuel vapor is purged from the car-
bon element by intake airflow and consumed in the nor-
mal combustion process.
Gasoline vapors from the fuel tank flow into the tube la-
beled TANK. These vapors are absorbed into the car-
bon. The canister is purged by 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 controlled
charcoal canister purge solenoid valve. This valve is
Pulse Width Modulated (PWM) or turned on and off sev-
eral times a second. The controlled charcoal canister
purge PWM duty cycle varies according to operating
conditions determined by mass airflow, fuel trim, and in-
take air temperature.
Poor idle, stalling, and poor driveability can be caused
by the following conditions:

An inoperative controlled canister purge valve.

A damaged canister.

Hoses that are split, cracked, or not connected to the
proper tubes.
CONTROLLED CHARCOAL
CANISTER
The controlled charcoal canister is an emission control
device containing activated charcoal granules. The con-
trolled charcoal canister is used to store fuel vapors from
the fuel tank. Once certain conditions are met, the En-
gine Control Module (ECM) activates the controlled
charcoal canister purge solenoid, allowing the fuel va-
pors to be drawn into the engine cylinders and burned.
POSITIVE CRANKCASE
VENTILATION CONTROL SYSTEM
OPERATION
A Positive Crankcase Ventilation (PCV) control system
is used to provide complete use of the crankcase va-

ENGINE CONTROLS 1F–7
DAEWOO M-150 BL2
manifold to decrease combustion temperature. The
amount of exhaust gas recirculated is controlled by vari-
ations in vacuum 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 EEGR valve is usually open under the following
conditions:

Warm engine operation.

Above idle speed.
Results of Incorrect Operation
Too much EEGR flow tends to weaken combustion,
causing the engine to run roughly or to stop. With too
much EEGR 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 EEGR valve stays open all the time, the engine
may not idle. Too little or no EEGR flow allows combus-
tion temperatures to get too high during acceleration
and load conditions. This could cause the following con-
ditions:

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 tempera-
ture of the air entering the engine. Low temperature pro-
duces a high resistance (100 kohms at –40C [–40F]),
while high temperature causes a low resistance (70
ohms at 130C [266F]).
The Engine Control Module (ECM) provides 5 volts to
the IAT sensor through a resistor in the ECM and mea-
sures 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
and readjust the stop screw. Misadjustment may result
in damage 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 volt-
age 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 con-
trols the airflow around the throttle valves which, in turn,
control the engine idle speed.
The desired idle speeds for all engine operating condi-
tions 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 calcu-
lated based on these memory values. As a result, en-
gine variations due to wear and variations in the
minimum throttle valve position (within limits) do not af-
fect 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 accel-
erator when starting until the ECM relearns idle control.
Engine idle speed is a function of total airflow into the
engine based on the IAC valve pintle position, the
throttle valve opening, and the calibrated vacuum loss
through accessories. The minimum throttle valve posi-
tion is set at the factory with a stop screw. This setting
allows enough airflow 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 op-
eration. The minimum throttle valve position setting on
this engine should not be considered the “minimum idle
speed,” as on other fuel injected engines. The throttle
stop screw is covered with a plug at the factory following
adjustment.
If the IAC valve is suspected as being the cause of im-
proper idle speed, refer to “Idle Air Control System
Check” in this section.
MANIFOLD ABSOLUTE PRESSURE
SENSOR
The Manifold Absolute Pressure (MAP) sensor mea-
sures the changes in the intake manifold pressure which
result from engine load and speed changes and con-
verts 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 pres-
sure. This is performed as part of MAP sensor calcula-