2006 Mazda 6 Check Engine light came on and took to repair shop, they said code P0128. Mechanic says to replace the Thermostat, the Cooling Sensor and water pump.

Price $690

Noticed before the check engine light came on the the cooling fan would come on and stay on even when starting for 1st time in the mornings when the engine is cold.

Is that about the going price to change items listed and is it possible the cooling fan staying on could actually be the problem

The Mazda dealer wants $125 for diagnostic check. Have thought about paying the $125 and going from there

 

Yes it could. If you can get access to a scanner that has a live data feature, pull up the Engine Temp Sensor data and watch it as the engine warms up. A bad T-Stat will normally keep the engine temp low, 158F ish.

Does the fan run, engine cold, with defrost/heat controls in the Off position? If so, that could definitely cause poor thermostat performance which sets the P0128. There was a campaign or TSB for the fan control module on certain year 6's and I think yours was in the mix.