Circuit Description
WARNING: This page is about a different car, the 2003 Lexus LS 430. However, it is still accessible from the selected car via links, so may be relevant.
ECM monitors vehicle speed, outside air temperature and engine load, and compares that information to engine coolant temperature. If engine coolant temperature does not reach 167°F (75°C), DTC P0128 will set. Possible causes are:
- Faulty thermostat.
- Cooling system not functioning properly.
- Faulty coolant temperature sensor.
- Faulty ECM.