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DRIVEABILITY - NGC
P0128-THERMOSTAT RATIONALITY —
TEST
2
NOTE: If a Engine Coolant Temperature (ECT) DTC is set along with this
code, diagnose the ECT DTC first.
NOTE: Inspect the ECT terminals and related PCM terminals. Ensure the
terminals are free from corrosion and damage.
NOTE: The best way to diagnose this DTC is to allow the vehicle to sit
overnight outside in order to have a totally cold soaked engine.
Note: Extremely cold outside ambient temperatures may have caused this
DTC to set.
WARNING: Never open the cooling system when the engine is hot. The
system is under pressure. Extreme burns or scalding may result. Allow the
engine to cool before opening the cooling system.
Check the coolant system to make sure that the coolant is in good condition and at
the proper level.
Is the coolant level and condition OK?
Yes → Go To 3
→ Inspect the vehicle for a coolant leak and add the necessary
No
3
Using the appropriate service information, determine the proper opening tempera-
ture of the thermostat.
NOTE: It is important that the thermostat meets all OEM specifications. An
incorrect thermostat or an improperly installed thermostat will cause this
DTC to set.
NOTE: This test works best if performed on a cold engine (cold soak).
Ignition on, engine not running.
With the DRBIII , monitor the Engine Coolant temperature. If the engine was
allowed to sit overnight (cold soak), the temperature value should be a sensible value
that is somewhere close to the ambient temperature.
NOTE: If engine coolant temperature is above 82°C (180°F), allow the engine
to cool until 65°C (150°F) is reached.
Start the Engine.
During engine warm-up, monitor the ECT Deg value on the DRBIII . The temper-
ature change should be a smooth transition from start up to normal operating temp
82°C (180°F) . Also monitor the actual coolant temperature with a thermometer.
NOTE: As the engine warms up to operating temperature, the actual coolant
temperature (thermometer reading) and the ECT Deg on the DRBIII
should stay within 10° (18°F) of each other.
If the thermostat does not open at the proper temperature, replace the thermostat.
If the monitored Engine Coolant Temperature transition from cold to hot was not
smooth or if the temperature value on the DRBIII was not within 10°C (18°F) of the
thermometer reading during warm-up, replace the ECT Sensor.
Were any problems found?
Yes → Repair as necessary.
→ Go To 4
No
4
Turn the ignition on.
With the DRBIII , read and record the AAT Sensor Temperature value
Using the DRB Temperature Probe #CH7050, measure the ambient air temperature
near the AAT sensor.
Is the AAT Sensor value with -15°C (5°F) of the temperature probe reading?
Yes → Go To 5
→ Go To 7
No
ACTION
amount of coolant.
Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC.
Perform POWERTRAIN VERIFICATION TEST VER - 5 - NGC.
Continued
82
APPLICABILITY
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