Infiniti FX35, FX50 (S51). Manual - part 663

P0125 ECT SENSOR

EC-193

< DTC/CIRCUIT DIAGNOSIS >

[VQ35HR]

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P0125 ECT SENSOR

Description

INFOID:0000000005236795

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 electrical resistance of the ther-
mistor decreases as temperature increases.

<Reference data>

*: These data are reference values and are measured between ECM terminals 71
(Engine coolant temperature sensor) and 84 (Sensor ground).

DTC Logic

INFOID:0000000005236796

DTC DETECTION LOGIC

NOTE:
• If DTC P0125 is displayed with DTC P0117 or P0118, first perform the trouble diagnosis for DTC

P0117, P0118. Refer to 

EC-186, "DTC Logic"

.

• If DTC P0125 is displayed with DTC P0116, first perform the trouble diagnosis for DTC P0116. Refer

to 

EC-184, "DTC Logic"

.

DTC CONFIRMATION PROCEDURE

1.

PRECONDITIONING

If DTC Confirmation Procedure has been previously conducted, always perform the following procedure
before conducting the next test.
1.

Turn ignition switch OFF and wait at least 10 seconds.

2.

Turn ignition switch ON.

3.

Turn ignition switch OFF and wait at least 10 seconds.

>> GO TO 2.

2.

CHECK ENGINE COOLANT TEMPERATURE SENSOR FUNCTION

With CONSULT-III

1.

Turn ignition switch ON.

SEF594K

Engine coolant temperature

[

°

C (

°

F)]

Voltage*

(V)

Resistance

(k

Ω

)

–10 (14)

4.4

7.0 - 11.4

20 (68)

3.5

2.37 - 2.63

50 (122)

2.2

0.68 - 1.00

90 (194)

0.9

0.236 - 0.260

SEF012P

DTC No.

Trouble diagnosis name

DTC detecting condition

Possible cause

P0125

Insufficient engine cool-
ant 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

EC-194

< DTC/CIRCUIT DIAGNOSIS >

[VQ35HR]

P0125 ECT SENSOR

2.

Select “DATA MONITOR” mode with CONSULT-III.

3.

Check that “COOLAN TEMP/S” is above 10

°

C (50

°

F).

With GST

Follow the procedure “With CONSULT-III” above.

Is the temperature above 10

°

C (50

°

F)?

YES

>> INSPECTION END

NO

>> GO TO 3.

3.

PERFORM DTC CONFIRMATION PROCEDURE

With CONSULT-III

1.

Start engine and run it for 65 minutes at idle speed.
If “COOLAN TEMP/S” increases to more than 10

°

C (50

°

F) within 65 minutes, stop engine because

the test result will be OK.

CAUTION:

Never overheat engine.

2.

Check 1st trip DTC.

With GST

Follow the procedure “With CONSULT-III” above.

Is 1st trip DTC detected?

YES

>>

EC-194, "Diagnosis Procedure"

NO

>> INSPECTION END

Diagnosis Procedure

INFOID:0000000005236797

1.

CHECK GROUND CONNECTION

1.

Turn ignition switch OFF.

2.

Check ground connection M95. Refer to Ground Inspection in 

GI-39, "Circuit Inspection"

.

Is the inspection result normal?

YES

>> GO TO 2.

NO

>> Repair or replace ground connection.

2.

CHECK ENGINE COOLANT TEMPERATURE SENSOR

Refer to 

EC-194, "Component Inspection"

.

Is the inspection result normal?

YES

>> GO TO 3.

NO

>> 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 that the

engine coolant does not flow.

Is the inspection result normal?

YES

>> GO TO 4.

NO

>> Repair or replace thermostat. Refer to 

CO-22, "Removal and Installation"

.

4.

CHECK INTERMITTENT INCIDENT

Refer to 

GI-36, "Intermittent Incident"

.

>> INSPECTION END

Component Inspection

INFOID:0000000005236798

1.

CHECK ENGINE COOLANT TEMPERATURE SENSOR

1.

Turn ignition switch OFF.

2.

Disconnect engine coolant temperature sensor harness connector.

3.

Remove engine coolant temperature sensor.

P0125 ECT SENSOR

EC-195

< DTC/CIRCUIT DIAGNOSIS >

[VQ35HR]

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4.

Check resistance between engine coolant temperature sensor
terminals by heating with hot water as shown in the figure.

Is the inspection result normal?

YES

>> INSPECTION END

NO

>> Replace engine coolant temperature sensor.

Terminals

Condition

Resistance (k

Ω

)

1 and 2

Temperature [

°

C (

°

F)]

20 (68)

2.37 - 2.63

50 (122)

0.68 - 1.00

90 (194)

0.236 - 0.260

JMBIA0080ZZ

EC-196

< DTC/CIRCUIT DIAGNOSIS >

[VQ35HR]

P0127 IAT SENSOR

P0127 IAT SENSOR

Description

INFOID:0000000005236799

The intake air temperature sensor is built-into the mass air flow sen-
sor (1). 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 rise in temperature.
NOTE:
ECM uses only the intake air temperature sensor (bank 1) for engine
control and self-diagnosis. It does not use the intake air temperature
sensor (bank 2).

<Reference data>

*: These data are reference values and are measured between ECM terminals 67
(Intake air temperature sensor) and 68 (Sensor ground).

DTC Logic

INFOID:0000000005236800

DTC DETECTION LOGIC

DTC CONFIRMATION PROCEDURE

1.

PRECONDITIONING

If DTC Confirmation Procedure has been previously conducted, always perform the following procedure
before conducting the next test.
1.

Turn ignition switch OFF and wait at least 10 seconds.

2.

Turn ignition switch ON.

3.

Turn ignition switch OFF and wait at least 10 seconds.

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.

>> GO TO 2.

2.

PERFORM DTC CONFIRMATION PROCEDURE

With CONSULT-III

1.

Wait until engine coolant temperature is less than 96

°

C (205

°

F)

-

Turn ignition switch ON.

-

Select “DATA MONITOR” mode with CONSULT-III.

-

Check the engine coolant temperature.

PBIA9559J

Intake air temperature

[

°

C (

°

F)]

Voltage*

(V)

Resistance

(k

Ω

)

25 (77)

3.3

1.800 - 2.200

80 (176)

1.2

0.283 - 0.359

SEF012P

DTC No.

Trouble diagnosis name

DTC detecting condition

Possible cause

P0127

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