On my smartcraft it says Ambient Temp Ckt HI, what to do?

//Jimmy

If it is referring to the Intake air temperature sensor circut, Check the connections on the Intake air sensor on the back of the intake. If the connection and sensor are connected and the code does not clear and stay off , then replace the sensor itself. Its actually a GM intake air sensor and can be purchased from GM or parts houses for a lot less than Mercury.

Best Regards,
Ray @ Raylar