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Home >> Lexus >> 2017 >> RC 300 F Sport >> Repair and Diagnosis >> External Pages >> Different car >> Section 31 (Engine Control System (8AR-FTS) - Diagnostic Codes (02 Of 10)) >> 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 [09/2020 - ] >> 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 [09/2020 - ]: Description

WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2024 Lexus RC 300, 2023 Lexus RC 300, 2022 Lexus RC 300, 2021 Lexus RC 300, and 2020 Lexus RC 300. 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, 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):
  1. Cold start.
  2. The engine is warmed up.
  3. The engine coolant temperature is less than 75°C (167°F).
  • Thermostat
  • Engine cooling system
  • 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 3 times (2 trip detection logic):
  1. The engine coolant temperature is less than 75°C (167°F).
  2. The value of the change in engine coolant temperature is less than the threshold.
  • Thermostat
  • Engine cooling system
  • Engine coolant temperature sensor
  • ECM
 Comes on DTC stored SAE Code: P0128
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