2001 INFINITI QX4 ignition

DescriptionNBEC0074NOTE:
If DTC P0120 is displayed with DTC P0510, first perform the trouble diagnosis for DTC P0510. Refer to
EC-431.
COMPONENT DESCRIPTIONNBEC0074S01The throttle position sensor responds to the accelerator pedal movement. This sensor is a kind of potentiom-
eter which transforms the throttle position into output voltage, and emits the voltage signal to the ECM. In
addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal
to the ECM.
Idle position of the throttle valve is determined by the ECM receiving the signal from the throttle position sen-
sor. This sensor controls engine operation such as fuel cut. On the other hand, the ªWide open and closed
throttle position switchº, which is built into the throttle position sensor unit, is not used for engine control.
AEC929
CONSULT-II Reference Value in Data Monitor
Mode
NBEC0075Specification data are reference values.
MONITOR ITEM CONDITION SPECIFICATION
THRTL POS SENIEngine: After warming up, idle
the engineThrottle valve: fully closed 0.15 - 0.85V
IEngine: After warming up
IIgnition switch: ON
(Engine stopped)Throttle valve: fully opened 3.5 - 4.7V
ABSOL TH´P/SIEngine: After warming up, idle
the engineThrottle valve: fully closed 0.0%
IEngine: After warming up
IIgnition switch: ON
(Engine stopped)Throttle valve: fully opened Approx. 80%
DTC P0120 THROTTLE POSITION SENSOR
Description
EC-174

ECM Terminals and Reference Value=NBEC0651Specification 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)
91 R Throttle position sensor[Engine is running]
IWarm-up condition
IAccelerator pedal fully released0.15 - 0.85V
[Ignition switch ªONº]
IAccelerator pedal fully depressed3.5 - 4.7V
111 P/B Sensors' power supply[Ignition switch ªONº]Approximately 5V
58 B/P Sensors' ground[Engine is running]
IWarm-up condition
IIdle speedApproximately 0V
On Board Diagnosis LogicNBEC0077Malfunction is detected when
(Malfunction A)an excessively low or high voltage from the sen-
sor is sent to ECM,
(Malfunction B)a high voltage from the sensor is sent to ECM
under light load driving conditions,
(Malfunction C)a low voltage from the sensor is sent to ECM
under heavy load driving conditions.
FAIL-SAFE MODENBEC0077S02When the malfunction A is detected, the ECM enters fail-safe mode
and the MIL lights up.
Detected items Engine operating condition in fail-safe mode
Throttle position sensor
circuitThrottle position will be determined based on the injected fuel amount and the engine speed.
Therefore, acceleration will be poor.
Condition Driving condition
When engine is idling Normal
When accelerating Poor acceleration
Possible CauseNBEC0430MALFUNCTION ANBEC0430S01IHarness or connectors
(The throttle position sensor circuit is open or shorted.)
IThrottle position sensor
MALFUNCTION BNBEC0430S02IHarness or connectors
(The throttle position sensor circuit is open or shorted.)
IThrottle position sensor
IFuel injector
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DTC P0120 THROTTLE POSITION SENSOR
ECM Terminals and Reference Value
EC-175

ICrankshaft position sensor (REF)
ICrankshaft position sensor (POS)
IMass air flow sensor
MALFUNCTION CNBEC0430S03IHarness or connectors
(The throttle position sensor circuit is open or shorted.)
IIntake air leaks
IThrottle position sensor
DTC Confirmation ProcedureNBEC0078NOTE:
IPerform ªPROCEDURE FOR MALFUNCTION Aº first. If the
1st trip DTC cannot be confirmed, perform ªPROCEDURE
FOR MALFUNCTION Bº.
If there is no problem on ªPROCEDURE FOR MALFUNC-
TION Bº, perform ªPROCEDURE FOR MALFUNCTION Cº.
IIf ªDTC Confirmation Procedureº has been previously
conducted, always turn ignition switch ªOFFº and wait at least
10 seconds before conducting the next test.
PROCEDURE FOR MALFUNCTION ANBEC0078S01CAUTION:
Always drive vehicle at a safe speed.
TESTING CONDITION:
IBefore performing the following procedure, confirm that
battery voltage is more than 10V at idle.
IThis test may be conducted with the drive wheels lifted in
the shop or by driving the vehicle. If a road test is
expected to be easier, it is unnecessary to lift the vehicle.
SEF065Y
With CONSULT-IINBEC0078S01011) Turn ignition switch ªONº and select ªDATA MONITORº mode
with CONSULT-II.
2) Start engine and maintain the following conditions for at least
5 consecutive seconds.
Vehicle speed More than 5 km/h (3 MPH)
Selector lever Suitable position except ªPº or ªNº position
3) If 1st trip DTC is detected, go to ªDiagnostic Procedureº,
EC-181.
With GSTNBEC0078S0102Follow the procedure ªWith CONSULT-IIº above.
DTC P0120 THROTTLE POSITION SENSOR
Possible Cause (Cont'd)
EC-176

SEF058Y
PROCEDURE FOR MALFUNCTION BNBEC0078S02With CONSULT-IINBEC0078S02011) Turn ignition switch ªONº.
2) Select ªDATA MONITORº mode with CONSULT-II.
3) Start engine and let it idle for at least 10 seconds.
If idle speed is over 1,000 rpm, maintain the following condi-
tions for at least 10 seconds to keep engine speed below 1,000
rpm.
Selector lever Suitable position except ªPº or ªNº
Brake pedal Depressed
Vehicle speed 0 km/h (0 MPH)
4) If 1st trip DTC is detected, go to ªDiagnostic Procedureº,
EC-181.
With GSTNBEC0078S0202Follow the procedure ªWith CONSULT-IIº above.
SEF177Y
PROCEDURE FOR MALFUNCTION CNBEC0078S03CAUTION:
Always drive vehicle at a safe speed.
With CONSULT-IINBEC0078S03011) Start engine and warm it up to normal operating temperature.
2) Turn ignition switch ªOFFº and wait at least 10 seconds.
3) Turn ignition switch ªONº.
4) Select ªMANU TRIGº in ªDATA MONITORº mode with CON-
SULT-II.
5) Select ªTHRTL POS SENº and ªABSOL TH´P/Sº in ªDATA
MONITORº mode with CONSULT-II.
6) Press RECORD on CONSULT-II SCREEN at the same time
accelerator pedal is depressed.
7) Print out the recorded graph and check the following:
IThe voltage rise is linear in response to accelerator pedal
depression.
IThe voltage when accelerator pedal is fully depressed is
approximately 4V.
If NG, go to ªDiagnostic Procedureº, EC-181.
If OK, go to following step.
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DTC P0120 THROTTLE POSITION SENSOR
DTC Confirmation Procedure (Cont'd)
EC-177

Diagnostic ProcedureNBEC0080
1 INSPECTION START
Which malfunction A, B or C is duplicated?
MTBL0066
TypeA,BorC
TypeAor B©GO TO 4.
Type C©GO TO 2.
2 ADJUST THROTTLE POSITION SENSOR
Check the following items. Refer to ªBasic Inspectionº, EC-101.
MTBL0655
©GO TO 3.
3 CHECK INTAKE SYSTEM.
1. Turn ignition switch ªOFFº.
2. Check the following for connection.
IAir duct
IVacuum hoses
IIntake air passage between air duct to intake manifold collector
OK or NG
OK©GO TO 4.
NG©Reconnect the parts.
4 RETIGHTEN GROUND SCREWS
1. Turn ignition switch ªOFFº.
2. Loosen and retighten engine ground screws.
SEF959Y
©GO TO 5.
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DTC P0120 THROTTLE POSITION SENSOR
Diagnostic Procedure
EC-181

5 CHECK THROTTLE POSITION SENSOR POWER SUPPLY CIRCUIT
1. Disconnect throttle position sensor harness connector.
SEF944Y
2. Turn ignition switch ªONº.
3. Check voltage between throttle position sensor terminal 1 and ground with CONSULT-II or tester.
SEF964Y
OK or NG
OK©GO TO 6.
NG©Repair open circuit or short to ground or short to power in harness or connectors.
6 CHECK THROTTLE POSITION SENSOR GROUND CIRCUIT FOR OPEN AND SHORT
1. Turn ignition switch ªOFFº.
2. Check harness continuity between sensor terminal 3 and engine ground.
Refer to Wiring Diagram.
Continuity should exist.
3. Also check harness for short to power.
OK or NG
OK©GO TO 8.
NG©GO TO 7.
7 DETECT MALFUNCTIONING PART
Check the following.
IHarness for open or short between ECM and throttle position sensor
IHarness for open or short between TCM (Transmission Control Module) and throttle position sensor
©Repair open circuit or short to power in harness or connectors.
DTC P0120 THROTTLE POSITION SENSOR
Diagnostic Procedure (Cont'd)
EC-182

8 CHECK THROTTLE POSITION SENSOR INPUT SIGNAL CIRCUIT FOR OPEN AND SHORT
1. Disconnect ECM harness connector.
2. Check harness continuity between ECM terminal 91 and throttle position sensor terminal 2.
Refer to Wiring Diagram.
Continuity should exist.
3. Also check harness for short to ground and short to power.
OK or NG
OK (With CONSULT-II)©GO TO 9.
OK (Without CONSULT-
II)©GO TO 10.
NG©Repair open circuit or short to ground or short to power in harness or connectors.
9 CHECK THROTTLE POSITION SENSOR
With CONSULT-II
1. Start engine and warm it up to normal operating temperature.
2. Stop engine (ignition switch OFF).
3. Remove the vacuum hose connected to the throttle opener.
4. Connect suitable vacuum hose to the vacuum pump and the opener.
5. Apply vacuum [more than ±40.0kPa (±300mmHg, ±11.81inHg)] until the throttle drum becomes free from the rod of the
throttle opener.
SEF793W
6. Turn ignition switch ON.
7. Select ªDATA MONITORº mode with CONSULT-II.
8. Check voltage of ªTHRTL POS SENº under the following conditions.
Voltage measurement must be made with throttle position sensor installed in vehicle.
SEF062Y
OK or NG
OK©GO TO 12.
NG©GO TO 11.
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DTC P0120 THROTTLE POSITION SENSOR
Diagnostic Procedure (Cont'd)
EC-183

10 CHECK THROTTLE POSITION SENSOR
Without CONSULT-II
1. Start engine and warm it up to normal operating temperature.
2. Stop engine (ignition switch OFF).
3. Remove the vacuum hose connected to the throttle opener.
4. Connect suitable vacuum hose to the vacuum pump and the opener.
5. Apply vacuum [more than þ40.0 kPa (þ300 mmHg, þ11.81 inHg)] until the throttle drum becomes free from the rod of
the throttle opener.
SEF793W
6. Turn ignition switch ON.
7. Check voltage between ECM terminal 91 (Throttle position sensor signal) and ground.
Voltage measurement must be made with throttle position sensor installed in vehicle.
MTBL0231
OK or NG
OK©GO TO 12.
NG©GO TO 11.
11 ADJUST CLOSED THROTTLE POSITION SWITCH
Adjust closed throttle position switch. Refer to ªBasic Inspectionº, EC-101.
MTBL0655
OK or NG
OK©GO TO 12.
NG©Replace throttle position sensor. To adjust it, perform ªBasic Inspectionº, EC-101.
DTC P0120 THROTTLE POSITION SENSOR
Diagnostic Procedure (Cont'd)
EC-184