Nissan Sentra Service Manual: P0128 Thermostat function

DTC Logic

DTC DETECTION LOGIC

NOTE:

If DTC P0128 is displayed with DTC P0300, P0301, P0302, P0303 or P0304, first perform the trouble diagnosis for P0300, P0301, P0302, P0303 or P0304. Refer to EC-269, "DTC Logic".

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 being stuck open.

DTC CONFIRMATION PROCEDURE

NOTE:

Never refuel before and during the following procedure.

1.PRECONDITIONING-1

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.PRECONDITIONING-2

With CONSULT

1. Turn ignition switch ON.
2. Check the following conditions

3. Select “DATA MONITOR” mode of “ENGINE” using CONSULT.
4. Check the following conditions:

Is the condition satisfied? YES >> GO TO 3.

NO >> 1. Satisfy the condition.

2. GO TO 3.

3.PERFORM DTC CONFIRMATION PROCEDURE-1

With CONSULT

1. Start engine.
2. Drive the vehicle until the following condition is satisfied.

CAUTION:

Always drive vehicle at safe speed.

• STEP 1

Drive the vehicle under the conditions instructed below until the difference between “COOLANT TEMP/S” and “FUEL T/TMP SE” becomes at least 26°C (47°F).

• STEP 2

Drive the vehicle at 50 km/h (32 MPH) or more with the difference between “COOLANT TEMP/S” and “FUEL T/TMP SE” maintained at 26°C (47°F) or more.

NOTE:

Keep the accelerator pedal as steady as possible during cruising.

• STEP 3

Drive the vehicle at 50 km/h (32 MPH) or more until “COOLANT TEMP/S” increases by 6°C (11°F).

NOTE:

Keep the accelerator pedal as steady as possible during cruising.

Is the condition satisfied? YES >> GO TO 4.

NO >> GO TO 1.

4.PERFORM DTC CONFIRMATION PROCEDURE-2

With CONSULT

1. Drive the vehicle until the following condition is satisfied.

CAUTION:

Always drive vehicle at safe speed.

2. Check 1st trip DTC.

Is 1st trip DTC detected? YES >> Proceed to EC-208, "Diagnosis Procedure".

NO >> INSPECTION END

Diagnosis Procedure

1.CHECK ENGINE COOLANT TEMPERATURE SENSOR

Check the engine coolant temperature sensor. Refer to EC-208, "Component Inspection".

Is the inspection result normal? YES >> GO TO 2.

NO >> Replace engine coolant temperature sensor. Refer to CO-24, "Exploded View".

2.CHECK THERMOSTAT

Check the thermostat. Refer to CO-21, "Removal and Installation of Thermostat".

Is the inspection result normal? YES >> INSPECTION END

NO >> Replace thermostat.

Component Inspection

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.
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. Refer to CO-24, "Exploded View".