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Home >> Lexus >> 2019 >> ES 350 Luxury >> Repair and Diagnosis >> External Pages >> Different car >> Section 223 (Engine Control System (A25A-FXS) - Diagnostic Codes (05 Of 20)) >> SFI System >> DTC P0128-00: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature); DTC P0128-07: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) Mechanical Failure [06/2018 - 08/2020] >> Description

DTC P0128-00: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature); DTC P0128-07: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) Mechanical Failure [06/2018 - 08/2020]: Description

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2024 Lexus ES 300h, 2023 Lexus ES 300h, 2022 Lexus ES 300h, 2021 Lexus ES 300h, and 2020 Lexus ES 300h. However, it is still accessible from the selected car via links, so may be relevant.

The ECM uses the engine coolant temperature sensor, installed to the water outlet, and the No. 2 engine coolant temperature sensor, installed to the radiator pipe assembly, to monitor the operation of the thermostat.

DTC No. Detection Item DTC Detection Condition Trouble Area MIL Memory Note
P0128-00 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) All of the following conditions are met for 5 seconds or more (2 trip detection logic):
  • The engine is started cold and then warmed up.
  • When the estimated engine coolant temperature is 75°C (167°F) or higher, the actual engine coolant temperature is less than 75°C (167°F).
  • Water inlet with thermostat sub-assembly (thermostat)
  • Cooling system
  • Engine coolant temperature sensor
  • No. 2 engine coolant temperature sensor
  • ECM
 Comes on DTC stored SAE Code: P0128
P0128-07 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) Mechanical Failure All of the following conditions are met for 30 seconds or more (2 trip detection logic):
  1. Water inlet housing with water pump sub-assembly is operating,
  2. The engine coolant temperature is less than 75°C (167°F).
  3. The difference between the rate of change of the engine coolant temperature sensor and No. 2 engine coolant temperature sensor is within the threshold.
  4. The difference between the temperature detected by the engine coolant temperature sensor and that detected by the No. 2 engine coolant temperature sensor is within the threshold.
  • Water inlet with thermostat sub-assembly (thermostat)
  • Cooling system
  • Engine coolant temperature sensor
  • No. 2 engine coolant temperature sensor
  • ECM
 Comes on DTC stored SAE Code: P0128
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