How To Fix Honda P0128 Code thermostat coolant temperature below thermostat regulating temperature

Definition meaning and fixes for a Honda P0128 engine Diagnostic Trouble Code: Coolant thermostat - coolant temperature below the thermostat regulating temperature. Cooling System Malfunction
Causes of a Honda P0128 DTC:
Low Coolant
Air in Coolant System
Bad Thermostat
Faulty Coolant Temperature Sensor
Coolant Temperature Sensor Wiring
Needs Software Update

[@user-zz4co7ph4u]

Thank you this helped

[@lisahaak1]

Can a loose hose attached to the thermostat housing on 2003 Honda pilot cause a whistling sound and po128 code? Already had the thermostat replaced and still getting code and whistling sound even when in park mode.

[@awadvcddf6981]

What was the solution to the problem?

[@deathstreak6259]

I have the code and replaced the sensor previously on my civic 2013. After 1 year its back and I know this time its the thermostat.

[@stevegordon2644]

I've had my thermostat and coolant temp sensor replaced on my 02 accord and the 128 code still comes back!!!! What the f should I do

[@whyingo7964]

If you have a scan tool, check what the coolant temp sensor is reading. If it is way off, check the wiring going to the sensor.

[@stevegordon2644]

@whyingo7964 I had a full engine diagnostic done. The guy said all my sensors are working said the Guage must be bad, called speedometer repair shop they said that wouldn't trip the check engine light. Idk