Subaru Legacy IV (2008 year). Manual - part 185

GD(H4SO)-42

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

Z: DTC P0126 INSUFFICIENT ENGINE COOLANT TEMPERATURE FOR STABLE 

OPERATION

1. OUTLINE OF DIAGNOSIS

Detect the malfunction of the engine coolant temperature sensor characteristics.
Memorize the engine coolant temperature and fuel temperature at the last engine stop, and use them to
judge as NG when the engine coolant temperature does not decrease when it should.

2. COMPONENT DESCRIPTION

3. ENABLE CONDITION

4. GENERAL DRIVING CYCLE

Perform the diagnosis only once after starting the engine.

(A)

Resistance value (k

:)

(B)

Temperature °C (°F)

 

 

 

 

 

 

 

 

(1)

Connector

(2)

Thermistor element

 

 

Secondary Parameters

Enable Conditions

Battery voltage

t 10.9 V

Refueling from the last engine stop till 
the current engine start

None

Fuel level

t 15 

2 (3.96 US gal, 

3.3 Imp gal)

Engine coolant temperature at the last 
engine stop

t 75 °C (167 °F)

EN-02917

(A)

(2)

(1)

(B)

GD(H4SO)-43

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

5. DIAGNOSTIC METHOD

• Abnormality Judgement

If the duration of time while the following conditions are met is longer than the time indicated, judge as NG.

Time Needed for Diagnosis: 2500 ms
Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cy-
cles.

• Normality Judgement

Judge as OK and clear the NG if the continuous time while the following conditions are established is more
than the predetermined time.

Time Needed for Diagnosis: Less than 1 second

Judgement Value

Malfunction Criteria

Threshold Value

Engine coolant temperature at the last 
engine stop — Minimum engine coolant 
temperature after the engine start

< 2.5 °C (36.5 °F)

Fuel temperature at the last engine stop 
— fuel temperature

t 5 °C (41 °F)

Intake air temperature — fuel temperature

< 2.5 °C (36.5 °F)

Fuel temperature

< 35 °C (95 °F)

Judgement Value

Malfunction Criteria

Threshold Value

Engine coolant temperature at the last 
engine stop — Minimum engine coolant 
temperature after the engine start

t 2.5 °C (36.5 °F)

GD(H4SO)-44

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

AA:DTC P0128 COOLANT THERMOSTAT (ENGINE COOLANT TEMPERATURE 

BELOW THERMOSTAT REGULATING TEMPERATURE)

1. OUTLINE OF DIAGNOSIS

Detect malfunctions of the thermostat function.
Judge as NG when the engine coolant temperature is lower than the estimated engine coolant temperature
and the difference between them is large. Judge as OK when the engine coolant temperature becomes to
75°C (167°F), and the difference is small, before judging NG.

2. COMPONENT DESCRIPTION

3. ENABLE CONDITION

4. GENERAL DRIVING CYCLE

Always perform the diagnosis continuously.

(1)

Valve

(4)

Piston

(7)

Stop ring

(2)

Spring

(5)

Guide

(8)

Wax element

(3)

Stopper

(6)

Rubber seal

(9)

Jiggle valve

Secondary Parameters

Enable Conditions

None

 

EN-01692

(9)

(2)

(6)

(8)

(7)

(5)

(4)

(3)

(1)

(2)

GD(H4SO)-45

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

5. DIAGNOSTIC METHOD

• Abnormality Judgement

If the duration of time while the following conditions are met is longer than the time indicated, judge as NG.

Time Needed for Diagnosis:64 ms × 3 time(s) × 152 time(s)
Malfunction Indicator Light Illumination:  Illuminates when malfunction occurs in 2 continuous driving cy-
cles.

• Normality Judgement

Judge as OK and clear the NG if the continuous time while the following conditions are established is more
than the predetermined time.

Time Needed for Diagnosis: Less than 1 second

Judgement Value

Malfunction Criteria

Threshold Value

Battery voltage

t 10.9 V

Estimate ambient temperature

t –7 °C (19.4 °F)

Thermostat malfunction diagnosis

Incomplete

Engine coolant temperature at engine 
starting

< 55 °C (131 °F)

Estimated coolant temperature

t 75 °C (167 °F)

Engine coolant temperature

d 75 °C (167 °F)

(Estimated – Measured) Engine coolant 
temperature

> 30 °C (86 °F)

Vehicle speed

t 30 km/h (18.6 MPH)

Judgement Value

Malfunction Criteria

Threshold Value

Battery voltage

t 10.9 V

Estimate ambient temperature

t –7 °C (19.4 °F)

Thermostat malfunction diagnosis

Incomplete

Engine coolant temperature at engine 
starting

< 55 °C (131 °F)

Engine coolant temperature

t 75 °C (167 °F)

(Estimated – Measured) Engine coolant 
temperature

d 30 °C (86 °F)