check engine DAEWOO MATIZ 2003 Service Owner's Manual

1E–12 ENGINE ELECTRICAL
DAEWOO M-150 BL2
BATTERY LOAD TEST
1. Check the battery for obvious damage, such as a
cracked or broken case or cover, which could permit
the loss of electrolyte. If obvious damage is noted, re-
place the battery.
Caution: Do not charge the battery if the hydrometer
is clear or light yellow. Instead, replace the battery. If
the battery feels hot or if violent gassing or spewing
of electrolyte through the vent hole occurs, discontin-
ue charging or reduce the charging rate to avoid inju-
ry.
2. Check the hydrometer. If the green dot is visible, go to
the load test procedure. If the indicator is dark but
green is not visible, charge the battery. For charging a
battery removed from the vehicle, refer to “Charging a
Completely Discharged Battery” in this section.
3. Connect a voltmeter and a battery load tester across
the battery terminals.
4. Apply a 300-ampere load for 15 seconds to remove
any surface charge from the battery.
5. Remove the load.
6. Wait 15 seconds to let the battery recover, and apply
a 270-ampere load.
Important: The battery temperature must be estimated
by touch and by the temperature condition the battery
has been exposed to for the preceding few hours.
7. If the voltage does not drop below the minimum
listed, the battery is good and should be reinstalled. If
the voltage is less than the minimum listed, replace
the battery. Refer to “Battery Specifications” in this
section.
GENERATOR OUTPUT TEST
1. Perform the generator system test. Refer to “Gener-
ator System Check” in this section.
2. Replace the generator if it fails that test. Refer to
“Generator” in the On-Vehicle Service section. If it
passes the test, perform the on-vehicle output
check which follows.
Important: Always check the generator for output be-
fore assuming that a grounded “L” terminal circuit has
damaged the regulator.
3. Attach a digital multimeter (a), an ammeter (b), and
a carbon pile load (c) to the battery (d) and the gen-
erator (e) of the rehicle.
D102E301
Important: Be sure the vehicle battery is fully charged,
and the carbon pile load is turned off.
4. With the ignition switch in the OFF position, check
and record the battery voltage.
5. Remove the harness connector from the generator.
6. Turn the ignition switch to the ON position with the
engine not running. Use a digital multimeter to
check for voltage in the harness connector “L” termi-
nal.
7. The reading should be near the specified battery
voltage of 12 volts. If the voltage is too low, check
the indicator “L” terminal circuits for open and
grounded circuits causing voltage loss. Correct any
open wires, terminal connections, etc., as neces-
sary. Refer to “Charging System” in this section.
8. Attach the generator harness connector.
9. Run the engine at a moderate idle, and measure the
voltage across the battery terminals. The reading
should be above that recorded in Step 4 but less
than 15 volts. If the reading is over 15 volts or below
the previous reading, replace the generator. Refer to
“Generator” in the On-Vehicle Service section.
10. Run the engine at a moderate idle, and measure the
generator amperage output.
11. Turn on the carbon pile, and adjust it to obtain the
maximum amps while maintaining the battery volt-
age above 13 volts.
12. If the reading is within 15 amps of the generator’s
rating noted on the generator, the generator is good.
If not, replace the generator. Refer to “Generator”
in the On-Vehicle Service section.
13. With the generator operating at the maximum out-
put, measure the voltage between the generator
housing and the battery negative terminal. The volt-
age drop should be 0.5 volt or less. If the voltage
drop is more than 0.5 volt, check the ground path
from the generator housing to the negative battery
cable.
14. Check, clean, tighten, and recheck all of the ground
connections.

ENGINE ELECTRICAL 1E–13
DAEWOO M-150 BL2
GENERATOR SYSTEM CHECK
When operating normally, the generator indicator lamp
will come on when the ignition switch is in the ON posi-
tion and go out when the engine starts. If the lamp oper-
ates abnormally or if an undercharged or overcharged
battery condition occurs, the following procedure may
be used to diagnose the charging system. Remember
that an undercharged battery is often caused by acces-
sories being left on overnight or by a defective switch
that allows a lamp, such as a trunk or glove box lamp, to
stay on.
Diagnose the generator with the following procedure:
1. Visually check the belt and wiring.
2. With the ignition switch in the ON position and the en-
gine stopped, the charge indicator lamp should be on.
If not, detach the harness at the generator and
ground the ‘‘L’’ terminal in the harness with a fused,
5-ampere jumper lead.
If the lamp lights, replace the generator. Refer to
“Generator” in the On-Vehicle Service section.

If the lamp does not light, locate the open circuit
between the ignition switch and the harness con-
nector. The indicator lamp bulb may be burned out.
3. With the ignition switch in the ON position and the en-
gine running at moderate speed, the charge indicator
lamp should be off. If not, detach the wiring harness
at the generator.

If the lamp goes off, replace the generator. Refer to
“Generator” in the On-Vehicle Service section.

If the lamp stays on, check for a short to ground in
the harness between the connector and the indica-
tor lamp.
Important: Always check the generator for output be-
fore assuming that a grounded ‘‘L’’ terminal circuit has
damaged the regulator. Refer to “Generator” in the Unit
Repair section.

ENGINE ELECTRICAL 1E – 19
DAEWOO M-150 BL2
REPAIR INSTRUCTIONS
UNIT REPAIR
D102E701
STARTER MOTOR
Inspection / Measurement
(Before the Overhaul)
1. Remove the starter. Refer to “Starter” in this section.
2. Pinion clearance inspection.

Disconnect the starter motor terminal M (1).

Connect the 12-volt battery lead to the starter mo-
tor terminals M and S.
Notice: Complete the testing in a minimum amount of
time to prevent overheating and damaging the solenoid.
(in 10 seconds)
D102E702

Switch on to move the pinion gear (2).

Now check the clearance between the pinion and
the stopper with the filler gauge (3).

If the clearance does not fall within the limits,
check for improper installation and replace all worn
parts.
D102E703
3. Magnetic switch pull-in test.

Disconnect the starter motor terminal M (1).

Connect the 12-volt battery lead to the starter mo-
tor terminals M and S.
Notice: Complete the testing in a minimum amount of
time to prevent overheating and damaging the solenoid.
(in 10 seconds)

1E–20 ENGINE ELECTRICAL
DAEWOO M-150 BL2
D102E704

Inspect the pinion gear’s moving to the outside (2).

If the pinion gear does not move outside, replace
the magnetic switch.
D102E705
4. Solenoid hold-in test.

Disconnect the starter motor terminal M (1).

Connect the 12-volt battery lead to the starter mo-
tor terminal S and body.
Notice: Complete the testing in a minimum amount of
time to prevent overheating and damaging the solenoid.
D102E706

Check the pinion gear’s moving to the outside (2).

If the pinion gear move to the inside, the circuit is
open. Replace the magnetic switch.
D102E707
5. Solenoid return test.

Disconnect the starter motor terminal M (1).

Connect the 12-volt battery lead to the starter mo-
tor terminal S and body.
Notice: Complete the testing in a minimum amount of
time to prevent overheating and damaging the solenoid.

ENGINE ELECTRICAL 1E–21
DAEWOO M-150 BL2
D102E708

Check the returning speed of pinion gear (2).
If the returning speed is fast, the operation is nor-
mal.

Replace the solenoid if the operation is abnormal.
D102E709
5. No-road test.

Connect the 12-volt battery lead to the starter cir-
cuit.

Connect the current and the voltage (1).

Install the starter motor rpm gage (2).

Start the starter motor with the switch on (3).

Measure the speed of pinion gear and the current.

If the measurement satisfy the limit, the starter mo-
tor is normal.
D102E710
DesciptionLimit
The speed of pinion
gearMinimum: 2,000 rpm
Condition:
Voltage/CurrentMaximum: 9V / 150A

Replace the starter motor if necessary.
D102E711
Disassembly Procedure
1. Remove the starter contact end frame.

Remove the through-bolts (1).

Remove the contact end frame bolts (2).

Remove the frame with the spacer (3).

ENGINE ELECTRICAL 1E–23
DAEWOO M-150 BL2
D102E716
Inspection / Measurement
(After the Overhaul)
1. Ground test for armature coil.

Inspect the insulation between commutator and ar-
mature coil using the voltmeter.

Replace the armature assembly if necessary.
D102E717
2. Short circuit test for armature coil.

If test equipment is available, check the armature
for short circuit by placing it on a growler, and hold-
ing back a saw blade over the armature core while
the armature is rotated. If the saw blade vibrates,
replace the armature.
D102E718
3. Open circuit test for armature coil.

Check the continuity between the commutator
bars using multimeter.

Replace the armature assembly if necessary.
D102E719
4. Inspect the brushes wear.

Inspect the brushes, the pop-out springs and the
brush holder for wear and damage. Replace the
brushes, if necessary.
a. Brushes wear limit.
DesciptionStandardLimit
Brushes wear11.3–11.5 mm
(0.445–0.453 in)7.0–7.25 mm
(0.275–0.285 in)

DAEWOO M-150 BL2
SECTION 1F
ENGINE CONTROLS
CAUTION: Disconnect the negative battery cable before removing or installing any electrical unit or when a
tool or equipment could easily come in contact with exposed electrical terminals. Disconnecting this cable
will help prevent personal injury and damage to the vehicle. The ignition must also be in LOCK unless
otherwise noted.
TABLE OF CONTENTS
Description and Operation 1F-4. . . . . . . . . . . . . . . . . .
Ignition System Operation 1F-4. . . . . . . . . . . . . . . . . .
Electronic Ignition System Ignition Coil 1F-4. . . . . . .
Crankshaft Position Sensor 1F-4. . . . . . . . . . . . . . . . .
Camshaft Position Sensor 1F-4. . . . . . . . . . . . . . . . . .
Idle Air System Operation 1F-4. . . . . . . . . . . . . . . . . .
Fuel Control System Operation 1F-4. . . . . . . . . . . . . .
Evaporative Emission Control System
Operation 1F-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Controlled Charcoal Canister 1F-5. . . . . . . . . . . . . . . .
Positive Crankcase Ventilation Control System
Operation 1F-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Engine Coolant Temperature Sensor 1F-6. . . . . . . . .
Throttle Position Sensor 1F-6. . . . . . . . . . . . . . . . . . . .
Catalyst Monitor Oxygen Sensors 1F-6. . . . . . . . . . .
Electric Exhaust Gas Recirculation Valve 1F-6. . . . .
Intake Air Temperature Sensor 1F-7. . . . . . . . . . . . . .
Idle Air Control Valve 1F-7. . . . . . . . . . . . . . . . . . . . . .
Manifold Absolute Pressure Sensor 1F-7. . . . . . . . . .
Engine Control Module 1F-8. . . . . . . . . . . . . . . . . . . . .
Fuel Injector 1F-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fuel Cutoff Switch (Inertia Switch) 1F-8. . . . . . . . . . .
Knock Sensor 1F-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Variable Reluctance (VR) Sensor 1F-8. . . . . . . . . . . .
Octane Number Connector 1F-8. . . . . . . . . . . . . . . . .
Strategy-Based Diagnostics 1F-9. . . . . . . . . . . . . . . .
EOBD Serviceability Issues 1F-9. . . . . . . . . . . . . . . . .
Serial Data Communications 1F-10. . . . . . . . . . . . . . .
Euro On-Board Diagnostic (EOBD) 1F-10. . . . . . . . .
Comprehensive Component Monitor Diagnostic
Operation 1F-11. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Common EOBD Terms 1F-11. . . . . . . . . . . . . . . . . . . .
DTC Types 1F-13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reading Diagnostic Trouble Codes 1F-13. . . . . . . . .
Primary System-Based Diagnostics 1F-15. . . . . . . . Diagnostic Information and Procedures 1F-17. . . .
System Diagnosis 1F-17. . . . . . . . . . . . . . . . . . . . . . . . . .
Diagnostic Aids 1F-17. . . . . . . . . . . . . . . . . . . . . . . . . .
Idle Learn Procedure 1F-17. . . . . . . . . . . . . . . . . . . . .
Euro On-Board Diagnostic (EOBD) System
Check 1F-18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ECM Output Diagnosis 1F-20. . . . . . . . . . . . . . . . . . . .
Multiple ECM Information Sensor DTCs Set 1F-21. .
Engine Cranks But Will Not Run 1F-25. . . . . . . . . . . .
No Malfunction Indicator Lamp 1F-30. . . . . . . . . . . . .
Malfunction Indicator Lamp On Steady 1F-32. . . . . .
Fuel System Diagnosis 1F-34. . . . . . . . . . . . . . . . . . . .
Fuel Pump Relay Circuit Check 1F-36. . . . . . . . . . . .
Main Relay Circuit Check 1F-38. . . . . . . . . . . . . . . . . .
Manifold Absolute Pressure Check 1F-40. . . . . . . . . .
Idle Air Control System Check 1F-42. . . . . . . . . . . . .
Ignition System Check 1F-45. . . . . . . . . . . . . . . . . . . .
Engine Cooling Fan Circuit Check 1F-48. . . . . . . . . .
Data Link Connector Diagnosis 1F-52. . . . . . . . . . . . .
Fuel Injector Balance Test 1F-54. . . . . . . . . . . . . . . . .
Diagnostic Trouble Code Diagnosis 1F-55. . . . . . . .
Clearing Trouble Codes 1F-55. . . . . . . . . . . . . . . . . . .
Diagnostic Trouble Codes 1F-55. . . . . . . . . . . . . . . . .
DTC P0107 Manifold Absolute Pressure Sensor
Low Voltage 1F-58. . . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0108 Manifold Pressure Sensor High
Voltage 1F-62. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0112 Intake Air Temperature Sensor Low
Voltage 1F-66. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0113 Intake Air Temperature Sensor High
Voltage 1F-68. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0117 Engine Coolant Temperature Sensor
Low Voltage 1F-72. . . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0118 Engine Coolant Temperature Sensor
High Voltage 1F-74. . . . . . . . . . . . . . . . . . . . . . . . . . .

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. . . . . . . . . . . . . . . . . . . .

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-