I have a MY01 2.5RS.

CEL came on couple days ago when I was driving down the Hwy. (I was probably going 85~90 mph)

So, I pulled the code w/ OBDII scanner, and it's P1490; Thermostat Malfunction.

I am not sure where to go from here. Is this mean I would have to replace the thermostat?

I have a ProECM Powerchip; is this could be a possible cause of the problem? After I installed the powerchip, I don't think the cooling fan turns on anymore. Even when I turn the A/C on while idling, cooling fan stays off.

Some help/comments would be appreciated. thanks.

 

change the thermostat and check the cooling temp sensor.
also put antifreeze at 50/50 the fan has to come on do not over heat the engine it will crack the block. hope this will help