P0128 Honda -Engine temp goes up to approx normal, is it the ECT then?

Question

check engine light on. engine temp guage shows normal temp so is it the ECT?

Answer 1

P0128 Thermostat below regulating temperature

This would more a thermostat problem than the ETC. Low coolant level  or coolant leaks can also set this code condition,

Here is a typical thermostat that set a P0128, what happens when a thermostat get stuck open it take longer for the engine management to go to closed loop. Closed loop is where the ECM uses information from the 02 sensor to maintain fuel control. When thermostat is stuck in the open position  it can easilty go into open loop, in open loop the ECM has to use look up tables or subsituted values to maintain fuel control