P0128 Honda Pilot
Coolant Thermostat Below Regulating Temperature · Powertrain Code · Medium · Repair: Easy
What is P0128?
The engine coolant is not reaching the expected temperature. Most commonly caused by a stuck-open thermostat, low coolant level, or a faulty coolant temperature sensor.
When the Honda Pilot triggers code P0128 (coolant thermostat below regulating temperature), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Honda Pilot.
This repair is rated easy, meaning basic tools, no lift needed.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Honda Pilot.
Common Causes on Honda Pilot
- Thermostat stuck open on 1.5T, 2.0T, or 3.5L V6 engine
- Thermostat housing gasket leak causing coolant weepage
- Coolant temperature sensor reading inaccurately
- Low coolant from radiator end tank seam leak
Symptoms
- Engine takes abnormally long to reach operating temperature
- Heater blows lukewarm or cold air
- Temperature gauge stays below normal or never reaches middle
- Slightly reduced fuel economy from extended open-loop operation
- Check engine light illuminated
Notes for Honda Pilot
CR-V and Pilot thermostat housing leaks are well-documented; check for external coolant stains.