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Home >> Lexus >> 2009 >> IS 250 RWD, Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> Testing & Diagnosis >> Engine Control System (DTCS P0010 - P0368) >> SFI System >> DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) >> Description

DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature): Description

This DTC is set when the Engine Coolant Temperature (ECT) does not reach 75°C (167°F) despite sufficient engine warm-up time.

DTC No. DTC Detection Condition Trouble Area
P0128 Conditions (a), (b) and (c) are met for 5 seconds (2 trip detection logic):
(a) Cold start
(b) Engine warmed up
(c) ECT less than 75°C (167°F)
  • Thermostat
  • Cooling system
  • ECT sensor
  • ECM