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Home >> Subaru >> 2017 >> Forester 2.0XT Touring >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Control System (Diagnostics) (P000A To P015B) (H4DOTC) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0128 Coolant Thermostat (Engine Coolant Temperature Below Thermostat Regulating Temperature) >> Diagnostic Method

Diagnostic Method

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

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value
When any one of the followings is established:
<Judgment 1>
Actual engine coolant temperature < 60°C (140°F)
and
Σ (Estimated engine coolant temperature - actual engine coolant temperature)
> Value of Map 3
<Judgment 2>
Actual engine coolant temperature < Regulated temperature* - Value of Map 4
and
Σ (Estimated engine coolant temperature - actual engine coolant temperature)
> Value of Map 5
*Regulated temperature = 89.2 degrees  
<Judgment 3>
Estimated engine coolant temperature - actual engine coolant temperature > 11.1°C (20°F)
and
Σ (Estimated engine coolant temperature - actual engine coolant temperature)
> Value of Map 6
MAP 3 SPECIFICATION

Engine coolant temperature at engine starting °C (°F) -7 (19.4) 0 (32) 10 (50) 25 (77) 30 (86) 40 (104)
Threshold Value °C (°F) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5) 961.5 (1730.7)
MAP 4 SPECIFICATION

Estimate ambient temperature °C (°F) -7 (19.4) 8 (46.4) 10 (50) 25 (77)
Threshold Value °C (°F) 18.6 (33.5) 11.1 (20) 11.1 (20) 11.1 (20)
MAP 5 SPECIFICATION

Engine coolant temperature at engine starting °C (°F) -7 (19.4) 0 (32) 8 (46.4) 10 (50) 30 (86) 35 (95)
Threshold Value °C (°F) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5) 1201.9 (2163.4)
MAP 6 SPECIFICATION

Engine coolant temperature at engine starting °C (°F) -7 (19.4) 8 (46.4) 10 (50) 25 (77)
Threshold Value °C (°F) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5) 1387.5 (2497.5)

Time needed for diagnosis:  Less than 1 second

Malfunction indicator light illumination:  Illuminates as soon as a malfunction occurs.