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Home >> Toyota >> 2009 >> Highlander Limited, FWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 18 (Engine Control System (1AR-FE) - DTC P0125 - P0500) >> DTC P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) >> Monitor Description

Monitor Description

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Fig 1: Engine Coolant Temperature Malfunction Graph
G06110958Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

The ECM estimates the engine coolant temperature based on the starting temperature, engine loads, and engine speeds. The ECM then compares the estimated temperature with the actual engine coolant temperature. When the estimated engine coolant temperature reaches 75°C (167°F), the ECM checks the actual engine coolant temperature. If the actual engine coolant temperature is less than 75°C (167°F), the ECM interprets this as a malfunction in the thermostat or the engine cooling system and stores the DTC.