2008 INFINITI QX56 check engine

P0122, P0123 TP SENSOREC-129
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Refer to
EC-86, "Ground Inspection" .
OK or NG
OK >> GO TO 2.
NG >> Repair or replace ground connections.
2.CHECK THROTTLE POSITION SENSOR 2 POWER SUPPLY CIRCUIT-I
1. Disconnect electric throttle c ontrol actuator harness connector.
2. Turn ignition switch ON.
3. Check voltage between electric throttle control actuator terminal 2 and ground with CONSULT-III or tester.
OK or NG
OK >> GO TO 7.
NG >> GO TO 3.
3.CHECK THROTTLE POSITION SENSOR 2 POWER SUPPLY CIRCUIT-II
1. Turn ignition switch OFF.
2. Disconnect ECM harness connector.
3. Check harness continuity between electric thrott le control actuator terminal 2 and ECM terminal 47.
Refer to Wiring Diagram.
OK or NG
OK >> GO TO 4.
NG >> Repair or replace open circuit.
4.CHECK THROTTLE POSITION SENSOR 2 POWER SUPPLY CIRCUIT-III
Check harness for short to power and short to ground, between the following terminals.
BBIA0354E
PBIB1480E
Voltage: Approximately 5V
PBIB2065E
Continuity should exist.
ECM terminalSensor terminal Reference Wiring Diagram
47 Electric throttle control actuator terminal 2 EC-439, "
Wiring Diagram - ENGINE
CONTROL SYSTEM -"91APP sensor terminal 6
Revision: March 2010 2008 QX56

EC-132
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P0125 ECT SENSOR
P0125 ECT SENSOR
Component DescriptionINFOID:0000000001351440
The engine coolant temperature sensor is used to detect the engine
coolant temperature. The sensor modifies a voltage signal from the
ECM. The modified signal returns to the ECM as the engine coolant
temperature input. The sensor uses
a thermistor which is sensitive to
the change in temperature. The elec trical resistance of the ther-
mistor decreases as temperature increases.

*: This data is reference value and is measured between ECM terminal 73 (Engine
coolant temperature sensor) and ground.
CAUTION:
Do not use ECM ground terminals when measuring input/output voltage. Doi ng so may result in dam-
age to the ECM's transistor. Use a ground ot her than ECM terminals, such as the ground.
On Board Diagnosis LogicINFOID:0000000001351441
DTC Confirmation ProcedureINFOID:0000000001351442
CAUTION:
Be careful not to overheat engine.
NOTE:
•If DTC P0125 is displayed with P0117 or P0118, first perform the trouble diagnosis for DTC P0117,
P0118. Refer to EC-125, "
DTC Confirmation Procedure".
• If DTC P0125 is displayed with P0116, first perf orm the trouble diagnosis for DTC P011. Refer to EC-
121, "DTC Confirmation Procedure".
• If DTC confirmation procedure has been previously conduc ted, always turn ignition switch OFF and wait at
least 10 seconds before conducting the next test.
WITH CONSULT-III
1. Turn ignition switch ON.
2. Select “DATA MONITOR” mode with CONSULT-III.
3. Check that “COOLAN TEMP/S” is above 31 °C (88° F).
If it is above 31° C (88°F), the test result will be OK.
If it is below 31 °C (88° F), go to following step.
SEF594K
Engine coolant temperature
°C ( °F) Voltage* V
Resistance kΩ
–10 (14) 4.47.0 - 11.4
20 (68) 3.52.1 - 2.9
50 (122) 2.20.68 - 1.00
90 (194) 0.90.236 - 0.260
SEF012P
DTC No. Trouble diagnosis name DTC detecting conditionPossible cause
P0125
0125 Insufficient engine coolant
temperature for closed loop
fuel control • Voltage sent to ECM from the sensor is not
practical, even when some time has passed
after starting the engine.
• Engine coolant temperature is insufficient for closed loop fuel control. • Harness or connectors
(High resistance in the circuit)
• Engine coolant temperature sensor
•Thermostat
Revision: March 2010 2008 QX56

P0125 ECT SENSOREC-133
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4. Start engine and run it for 65 minutes at idle speed.
If “COOLAN TEMP/S” increases to more than 31° C (88°F) within 65 minutes, stop engine because
the test result will be OK.
5. Check 1st trip DTC.
6. If 1st trip DTC is detected, go to EC-133, "
Diagnosis Procedure" .
WITH GST
Follow the procedure “WITH CONSULT-III” above.
Diagnosis ProcedureINFOID:0000000001351443
1.CHECK GROUND CONNECTIONS
1. Turn ignition switch OFF.
2. Loosen and retighten three ground screws on the body. Refer to EC-86, "
Ground Inspection" .
OK or NG
OK >> GO TO 2.
NG >> Repair or replace ground connections.
2.CHECK ENGINE COOLANT TEMPERATURE SENSOR
Refer to EC-133, "
Component Inspection" .
OK or NG
OK >> GO TO 3.
NG >> Replace engine coolant temperature sensor.
3.CHECK THERMOSTAT OPERATION
When the engine is cold [lower than 70 °C (158° F)] condition, grasp lower radiator hose and confirm the engine
coolant does not flow.
OK or NG
OK >> GO TO 4.
NG >> Repair or replace thermostat. Refer to CO-22, "
Removal and Installation" .
4.CHECK INTERMITTENT INCIDENT
Refer to GI-35, "
How to Check Terminal" and GI-38, "Intermittent Incident".
Refer to EC-439, "
Wiring Diagram - ENGINE CONTROL SYSTEM -" .
>> INSPECTION END
Component InspectionINFOID:0000000001351444
ENGINE COOLANT TEMPERATURE SENSOR
BBIA0354E
Revision: March 2010 2008 QX56

EC-134
< COMPONENT DIAGNOSIS >[VK56DE]
P0125 ECT SENSOR
1. Check resistance between engine coolant temperature sensor
terminals 1 and 2 as shown in the figure.

2. If NG, replace engine coolant temperature sensor.
PBIB2005E
Engine coolant temperature °C ( °F) Resistance kΩ
20 (68) 2.1 - 2.9
50 (122) 0.68 - 1.00
90 (194) 0.236 - 0.260
SEF012P
Revision: March 2010 2008 QX56

P0127 IAT SENSOREC-135
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P0127 IAT SENSOR
Component DescriptionINFOID:0000000001351446
The intake air temperature sensor is
built into mass air flow sensor.
The sensor detects intake air temperature and transmits a signal to
the ECM.
The temperature sensing unit uses a thermistor which is sensitive to
the change in temperature. Electrical resistance of the thermistor
decreases in response to the temperature rise.

*: This data is reference value and is measured between ECM terminal 34 (Intake air
temperature sensor) and ground.
CAUTION:
Do not use ECM ground terminals when measuring input/output
voltage. Doing so may result in damage to the ECM's transistor.
Use a ground other than ECM te rminals, such as the ground.
On Board Diagnosis LogicINFOID:0000000001351447
DTC Confirmation ProcedureINFOID:0000000001351448
NOTE:
If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at
least 10 seconds before conducting the next test.
CAUTION:
Always drive vehicle at a safe speed.
TESTING CONDITION:
This 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.
WITH CONSULT-III
1. Wait until engine coolant temperature is less than 90 °C (194 °F)
a. Turn ignition switch ON.
b. Select “DATA MONITOR” mode with CONSULT-III.
c. Check the engine coolant temperature.
d. If the engine coolant temperature is not less than 90 °C (194° F), turn ignition switch OFF and cool down
engine.
• Perform the following steps before engine coolant temperature is above 90 °C (194° F).
2. Turn ignition switch ON.
BBIA0355E
Intake air temperature °C ( °F) Voltage* V
Resistance kΩ
25 (77) 3.31.800 - 2.200
80 (176) 1.20.283 - 0.359
SEF012P
DTC No. Trouble diagnosis name DTC detecting condition Possible cause
P0127
0127 Intake air temperature
too high Rationally incorrect voltage from the sensor is
sent to ECM, compared with the voltage signal
from engine coolant temperature sensor. • Harness or connectors
(The sensor circuit is open or shorted)
• Intake air temperature sensor
Revision: March 2010 2008 QX56

EC-136
< COMPONENT DIAGNOSIS >[VK56DE]
P0127 IAT SENSOR
3. Select “DATA MONITOR” mode with CONSULT-III.
4. Start engine.
5. Hold vehicle speed at more than 70 km/h (43 MPH) for 100 consecutive seconds.
6. Check 1st trip DTC.
7. If 1st trip DTC is detected, go to
EC-136, "
Diagnosis Procedure" .
WITH GST
Follow the procedure “WITH CONSULT-III” above.
Diagnosis ProcedureINFOID:0000000001351449
1.CHECK GROUND CONNECTIONS
1. Turn ignition switch OFF.
2. Loosen and retighten three ground screws on the body. Refer to EC-86, "
Ground Inspection" .
OK or NG
OK >> GO TO 2.
NG >> Repair or replace ground connections.
2.CHECK INTAKE AIR TEMPERATURE SENSOR
Refer to EC-136, "
Component Inspection" .
OK or NG
OK >> GO TO 3.
NG >> Replace mass air flow sensor (with intake air temperature sensor).
3.CHECK INTERMITTENT INCIDENT
Refer to GI-35, "
How to Check Terminal" and GI-38, "Intermittent Incident".
Refer to EC-439, "
Wiring Diagram - ENGINE CONTROL SYSTEM -" .
>> INSPECTION END
Component InspectionINFOID:0000000001351450
INTAKE AIR TEMPERATURE SENSOR
1. Check resistance between intake air temperature sensor termi-
nals 5 and 6 under the following conditions.
2. If NG, replace mass air flow sens or (with intake air temperature
sensor).
BBIA0354E
Intake air temperature °C ( °F) Resistance k Ω
25 (77) 1.800 - 2.200
BBIA0355E
Revision: March 2010 2008 QX56

EC-138
< COMPONENT DIAGNOSIS >[VK56DE]
P0128 THERMOSTAT FUNCTION
P0128 THERMOSTAT FUNCTION
On Board Diagn
osis LogicINFOID:0000000001449652
NOTE:
If DTC P0128 is displayed with DTC P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307 or P0308,
first perform the trouble diagnosis for DTC P 0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307,
P0308. Refer to EC-198, "
DTC Confirmation Procedure".
Engine coolant temperature has not risen enough to open the thermostat even though the engine has run long
enough.
This is due to a leak in the seal or the thermostat stuck open.
DTC Confirmation ProcedureINFOID:0000000001449653
NOTE:
Check vehicle specifications and VIN, then select the procedure to be performed. (Refer to the table below.)
PROCEDURE A
With CONSULT-III
NOTE:
If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at
least 10 seconds before conducting the next test.
TESTING CONDITION:
•For best results, perform at ambient temperature of –10 °C (14° F) or higher.
• For best results, perform at en gine coolant temperature of –10 °C (14° F) to 71 °C (160 °F).
• Before performing the following procedure, do not fill with the fuel.
1. Turn A/C switch OFF.
2. Turn blower fan switch OFF.
3. Turn ignition switch ON.
4. Select “COOLAN TEMP/S” in “DATA MONITOR” mode with CONSULT-III.
5. Check the indication of “COOLAN TEMP/S”. If it is below 71 °C (160° F), go to following step.
If it is above 71 °C (160° F), cool down the engine to less than 71 °C (160° F). Then go to next steps.
6. Start engine and wait at idle for at least 30 minutes.
DTC No. Trouble diagnosis name DTC detecting condition Possible cause
P0128
0128 Thermostat function The engine coolant temperature does not
reach to specified temperature even though
the engine has run long enough. • Thermostat
• Leakage from sealing portion of thermostat
• Engine coolant temperature sensor
Vehicle specification Vehicle serial number
Procedure
2WD with ASCD Up to 327618
A
Between 327619 and 912536 B
From 912537 C
2WD with ICC Up to 327618
A
Between 327619 and 914347 B
From 914348 C
4WD with ASCD Up to 327618
A
Between 327619 and 913067 B
From 913068 C
4WD with ICC Up to 327618
A
Between 327619 and 912422 B
From 912423 C
Revision: March 2010 2008 QX56

P0128 THERMOSTAT FUNCTIONEC-139
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If “COOLAN TEMP/S” increases to more than 71°
C (160°F) within 30 minutes, turn ignition switch
OFF because the test result will be OK.
7. Check 1st trip DTC.
8. If 1st trip DTC is detected, go to EC-140, "
Diagnosis Procedure".
With GST
Follow the procedure “With CONSULT-III” above.
PROCEDURE B
With CONSULT-III
NOTE:
If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at
least 10 seconds before conducting the next test.
TESTING CONDITION:
•For best results, perform at ambient temperature of –10 °C (14° F) or higher.
• For best results, perform at engine coolant temperature of –10 °C (14° F) to 52 °C (126° F).
• Before performing the following pro cedure, do not fill with the fuel.
1. Turn A/C switch OFF.
2. Turn blower fan switch OFF.
3. Turn ignition switch ON.
4. Select “COOLAN TEMP/S” in “DAT A MONITOR” mode with CONSULT-III.
5. Check the indication of “COOLAN TEMP/S”. If it is below 52 °C (126 °F), go to following step.
If it is above 52 °C (126° F), cool down the engine to less than 52° C (126°F). Then go to next steps.
6. Start engine and wait at idle for at least 30 minutes. If “COOLAN TEMP/S” increases to more than 71° C (160°F) within 30 minutes, turn ignition switch
OFF because the test result will be OK.
7. Check 1st trip DTC.
8. If 1st trip DTC is detected, go to EC-140, "
Diagnosis Procedure".
With GST
Follow the procedure “With CONSULT-III” above.
PROCEDURE C
With CONSULT-III
NOTE:
If DTC Confirmation Procedure has been previously conducted, always turn ignition switch OFF and wait at
least 10 seconds before conducting the next test.
TESTING CONDITION:
•For best results, perform at ambient temperature of –10 °C (14° F) or higher.
• For best results, perform at engine coolant temperature of –10 °C (14° F) to 56 °C (133° F).
• Before performing the following pro cedure, do not fill with the fuel.
1. Turn A/C switch OFF.
2. Turn blower fan switch OFF.
3. Turn ignition switch ON.
4. Select “COOLAN TEMP/S” in “DAT A MONITOR” mode with CONSULT-III.
5. Check the indication of “COOLAN TEMP/S”. If it is below 56 °C (133 °F), go to following step.
If it is above 56 °C (133° F), cool down the engine to less than 56° C (133°F). Then go to next steps.
6. Start engine and wait at idle for at least 30 minutes. If “COOLAN TEMP/S” increases to more than 75° C (167°F) within 30 minutes, turn ignition switch
OFF because the test result will be OK.
7. Check 1st trip DTC.
8. If 1st trip DTC is detected, go to EC-140, "
Diagnosis Procedure".
Revision: March 2010 2008 QX56