2001 INFINITI QX4 Engine control

DescriptionNBEC0249SYSTEM DESCRIPTIONNBEC0249S01
Sensor Input Signal to ECMECM func-
tionActuator
Crankshaft position sensor (POS) Engine speed (POS signal)
Idle air
controlIACV-AAC valve Crankshaft position sensor (REF) Engine speed (REF signal)
Mass air flow sensor Amount of intake air
Engine coolant temperature sensor Engine coolant temperature
Ignition switch Start signal
Throttle position sensor Throttle position
Park/neutral position (PNP) switch Park/neutral position
Air conditioner switch Air conditioner operation
Power steering oil pressure switch Power steering load signal
Battery Battery voltage
Vehicle speed sensor Vehicle speed
Ambient air temperature switch Ambient air temperature
Intake air temperature sensor Intake air temperature
Absolute pressure sensor Ambient barometic pressure
This system automatically controls engine idle speed to a specified
level. Idle speed is controlled through fine adjustment of the
amount of air which by-passes the throttle valve via IACV-AAC
valve. The IACV-AAC valve changes the opening of the air by-pass
passage to control the amount of auxiliary air. This valve is actu-
ated by a step motor built into the valve, which moves the valve in
the axial direction in steps corresponding to the ECM output sig-
nals. One step of IACV-AAC valve movement causes the respec-
tive opening of the air by-pass passage. (i.e. when the step
advances, the opening is enlarged.) The opening of the valve is
varied to allow for optimum control of the engine idling speed. The
crankshaft position sensor (POS) detects the actual engine speed
and sends a signal to the ECM. The ECM then controls the step
position of the IACV-AAC valve so that engine speed coincides with
the target value memorized in ECM. The target engine speed is the
lowest speed at which the engine can operate steadily. The opti-
mum value stored in the ECM is determined by takig into consid-
eration various engine conditions, such as during warm up,
deceleration, and engine load (air conditioner, power steering and
cooling fan operation).
SEF765P
COMPONENT DESCRIPTIONNBEC0249S02IACV-AAC ValveNBEC0249S0201The IACV-AAC valve is operated by a step motor for centralized
control of auxiliary air supply. This motor has four winding phases
and is actuated by the output signals of ECM which turns ON and
OFF two windings each in seqeunce. Each time the IACV-AAC
valve opens or closes to change tha auxiliary air quantity, the ECM
sends a pulse signal to the step motor. When no change in the
auxiliary air quantity is needed, the ECM does not issue the pulse
signal. A certain voltage signal is issued so that the valve remains
at that particular opening.
DTC P0505 IDLE AIR CONTROL VALVE (IACV) Ð AUXILIARY AIR CONTROL
(AAC) VALVE
Description
EC-422

CONSULT-II Reference Value in Data Monitor
Mode
NBEC0250Specification data are reference values.
MONITOR ITEM CONDITION SPECIFICATION
IACV-AAC/VIEngine: After warming up
IAir conditioner switch: ªOFFº
IShift lever: ªNº
INo-loadIdle 14 - 20 step
2,000 rpm Ð
ECM Terminals and Reference ValueNBEC0670Specification data are reference values and are measured between each terminal and ground.
CAUTION:
Do not use ECM ground terminals when measuring input/output voltage. Doing so may result in dam-
age to the ECM's transistor. Use a ground other than ECM terminals, such as the ground.
TERMI-
NAL
NO.WIRE
COLORITEM CONDITION DATA (DC Voltage)
6
7
8
17PU/G
GY
Y
GY/LIACV-AAC valve[Engine is running]
IIdle speed0.1 - 14V
On Board Diagnosis LogicNBEC0252Malfunction is detected when
(Malfunction A)the IACV-AAC valve does not operate properly,
(Malfunction B)the IACV-AAC valve does not operate properly.
Possible CauseNBEC0515MALFUNCTION ANBEC0515S01IHarness or connectors
(The IACV-AAC valve circuit is open.)
IIACV-AAC valve
MALFUNCTION BNBEC0515S02IHarness or connectors
(The IACV-AAC valve circuit is shorted.)
IAir control valve (Power steering)
IIACV-AAC valve
DTC Confirmation ProcedureNBEC0253NOTE:
IIf ªDTC Confirmation Procedureº has been previously
conducted, always turn ignition switch ªOFFº and wait at least
10 seconds before conducting the next test.
IPerform ªPROCEDURE FOR MALFUNCTION Aº first. If 1st
trip DTC cannot be confirmed, perform ªPROCEDURE
FOR MALFUNCTION Bº.
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DTC P0505 IDLE AIR CONTROL VALVE (IACV) Ð AUXILIARY AIR CONTROL
(AAC) VALVE
CONSULT-II Reference Value in Data Monitor Mode
EC-423

SEF058Y
PROCEDURE FOR MALFUNCTION ANBEC0253S01TESTING CONDITION:
Before performing the following procedure, confirm that bat-
tery voltage is more than 10.5V with ignition switch ªONº.
With CONSULT-IINBEC0253S01011) Start engine and warm it up to normal operating temperature.
2) Turn ignition switch ªOFFº and wait at least 10 seconds.
3) Perform ªIdle Air Volume Learningº (see EC-57).
4) Turn ignition switch ªOFFº and wait at least 10 seconds.
5) Turn ignition switch ªONº.
6) Select ªDATA MONITORº mode with CONSULT-II.
7) Start engine and let it idle.
8) Keep engine speed at 2,500 rpm for three seconds, then let it
idle for three seconds.
Do not rev engine to more than 3,000 rpm.
9) Perform step 4 once more.
10) If 1st trip DTC is detected, go to ªDiagnostic Procedureº,
EC-426.
With GSTNBEC0253S0102Follow the procedure ªWith CONSULT-IIº above.
SEF174Y
PROCEDURE FOR MALFUNCTION BNBEC0253S02TESTING CONDITION:
IBefore performing the following procedure, confirm that
battery voltage is more than 11V at idle.
IAlways perform the test at a temperature above þ10ÉC
(14ÉF).
With CONSULT-IINBEC0253S02011) Open engine hood.
2) Start engine and warm it up to normal operating temperature.
3) Turn ignition switch ªOFFº and wait at least 10 seconds.
4) Perform ªIdle Air Volume Learningº (see EC-57).
5) Turn ignition switch ªOFFº and wait at least 10 seconds.
6) Turn ignition switch ªONº again and select ªDATA MONITORº
mode with CONSULT-II
7) Start engine and run it for at least 1 minute at idle speed.
8) If 1st trip DTC is detected, go to ªDiagnostic Procedureº,
EC-426.
With GSTNBEC0253S0202Follow the procedure ªWith CONSULT-IIº above.
DTC P0505 IDLE AIR CONTROL VALVE (IACV) Ð AUXILIARY AIR CONTROL
(AAC) VALVE
DTC Confirmation Procedure (Cont'd)
EC-424

Diagnostic ProcedureNBEC0255
1 CHECK IACV-AAC VALVE POWER SUPPLY CIRCUIT
1. Stop engine.
2. Disconnect IACV-AAC valve harness connector.
SEF994Y
3. Turn ignition switch ªONº.
4. Check voltage between IACV-AAC valve terminals 2, 5 and ground with CONSULT-II or tester.
SEF343X
OK or NG
OK©GO TO 3.
NG©GO TO 2.
2 DETECT MALFUNCTIONING PART
Check the following.
IHarness connectors E1, M1
IHarness connectors M33, F22
IHarness for open or short between IACV-AAC valve and ECM relay
©Repair harness or connectors.
DTC P0505 IDLE AIR CONTROL VALVE (IACV) Ð AUXILIARY AIR CONTROL
(AAC) VALVE
Diagnostic Procedure
EC-426

3 CHECK IACV-AAC VALVE OUTPUT SIGNAL CIRCUIT FOR OPEN AND SHORT
1. Turn ignition switch ªOFFº.
2. Disconnect ECM harness connector.
3. Check harness continuity between ECM terminals and IACV-AAC valve terminals as follows.
Refer to Wiring Diagram.
MTBL0354
Continuity should exist.
4. Also check harness for short to ground and short to power.
OK or NG
OK©GO TO 5.
NG©GO TO 4.
4 DETECT MALFUNCTIONING PART
Check the following.
IHarness connectors F101, F6
IHarness for open or short between IACV-AAC valve and ECM
©Repair harness connectors.
5 CHECK AIR CONTROL VALVE (POWER STEERING) OPERATION-I
1. Reconnect ECM harness connector and IACV-AAC valve harness connector.
2. Disconnect vacuum hose connected to air control valve (Power steering) at intake air duct.
3. Start engine and let it idle.
4. Check vacuum hose for vacuum existence.
SEF995Y
Vacuum slightly exists or does not exist.
OK or NG
OK©GO TO 6.
NG©Replace air control valve (Power steering).
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DTC P0505 IDLE AIR CONTROL VALVE (IACV) Ð AUXILIARY AIR CONTROL
(AAC) VALVE
Diagnostic Procedure (Cont'd)
EC-427

6 CHECK AIR CONTROL VALVE (POWER STEERING) OPERATION-II
Check vacuum hose for vacuum existence when steering wheel is turned.
SEF995Y
Vacuum should exist.
OK or NG
OK©GO TO 9.
NG©GO TO 7.
7 CHECK VACUUM PORT
1. Stop engine.
2. Disconnect vacuum hose connected to air control valve (Power steering) at vacuum port.
3. Blow air into vacuum port.
4. Check that air flows freely.
SEF996Y
OK or NG
OK©GO TO 8.
NG©Repair or clean vacuum port.
DTC P0505 IDLE AIR CONTROL VALVE (IACV) Ð AUXILIARY AIR CONTROL
(AAC) VALVE
Diagnostic Procedure (Cont'd)
EC-428

10 CHECK IACV-AAC VALVE-II
1. Reconnect IACV-AAC valve harness connector and ECM harness connector.
2. Turn ignition switch ªONº and ªOFFº, and ensure the IACV-AAC valve makes operating sound according to the ignition
switch position.
SEF997Y
OK or NG
OK©GO TO 12.
NG©GO TO 11.
11 REPLACE IACV-AAC VALVE
1. Replace IACV-AAC valve assembly.
2. Perform ªIdle Air Volume Learningº, EC-57.
Is the result CMPLT or INCMP?
CMPLT or INCMP
CMPLT©INSPECTION END
INCMP©Follow the construction of ªIdle Air Volume Learningº.
12 CHECK TARGET IDLE SPEED
1. Turn ignition switch ªOFFº.
2. Reconnect all harness connectors and vacuum hoses.
3. Start engine and warm it up to normal operating temperature.
4. Also warm up transmission to normal operating temperature.
IFor A/T models with CONSULT-II, drive vehicle until ªFLUID TEMP SEº in ªDATA MONITORº mode of ªA/Tº system indi-
cates less than 0.9V.
IFor A/T models without CONSULT-II, drive vehicle for 10 minutes.
5. Stop vehicle with engine running.
6. Check target idle speed.
A/T: 750±50 rpm (in ªPº or ªNº position)
OK or NG
OK©GO TO 13.
NG©Perform ªIdle Air Volume Learningº, EC-57.
13 CHECK INTERMITTENT INCIDENT
Refer to ªTROUBLE DIAGNOSIS FOR INTERMITTENT INCIDENTº, EC-140.
©INSPECTION END
DTC P0505 IDLE AIR CONTROL VALVE (IACV) Ð AUXILIARY AIR CONTROL
(AAC) VALVE
Diagnostic Procedure (Cont'd)
EC-430

SEF505V
Component DescriptionNBEC0256A closed throttle position switch and wide open throttle position
switch are built into the throttle position sensor unit. The wide open
throttle position switch is used only for A/T control.
When the throttle valve is in the closed position, the closed throttle
position switch sends a voltage signal to the ECM. The ECM only
uses this signal to open or close the EVAP canister purge volume
control solenoid valve when the throttle position sensor is malfunc-
tioning.
CONSULT-II Reference Value in Data Monitor
Mode
NBEC0257Specification data are reference values.
MONITOR ITEM CONDITION SPECIFICATION
CLSD THL/P SWIEngine: After warming up, idle
the engineThrottle valve: Idle position ON
Throttle valve: Slightly open OFF
ECM Terminals and Reference ValueNBEC0671Specification data are reference values and are measured between each terminal and ground.
CAUTION:
Do not use ECM ground terminals when measuring input/output voltage. Doing so may result in dam-
age to the ECM's transistor. Use a ground other than ECM terminals, such as the ground.
TERMI-
NAL
NO.WIRE
COLORITEM CONDITION DATA (DC Voltage)
56 OR/LThrottle position switch
(Closed position)[Engine is running]
IAccelerator pedal fully releasedBATTERY VOLTAGE
(11 - 14V)
[Engine is running]
IAccelerator pedal depressedApproximately 0V
On Board Diagnosis LogicNBEC0259Malfunction is detected when battery voltage from the closed
throttle position switch is sent to ECM with the throttle valve
opened.
Possible CauseNBEC0516IHarness or connectors
(The closed throttle position switch circuit is shorted.)
IClosed throttle position switch
IThrottle position sensor
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DTC P0510 CLOSED THROTTLE POSITION SWITCH
Component Description
EC-431