P0128 OBD II Trouble Code Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Symptoms of P0128 OBD II Trouble Code

  • Engine takes longer to warm up
  • Engine temperature drops while driving at higher speeds

Common Causes of P0128 OBD II Trouble Code

  • Low engine coolant level
  • Leaking or stuck open thermostat (likely)
  • Faulty cooling fan (running too much)
  • Faulty coolant temperature (ECT) sensor
  • Faulty intake air temperature (IAT) sensor