Hoses, Coolant, Thermostat and Sensor replaced. Now get Service Engine Soon light

[MarkNYC]

I just had a coolant service done on a 2001 Montana with 84,000 miles. It was the first time the system was flushed and filled since I bought it new. Temp gauge was not working but all was fine. I figured sensor was bad. Had trusted mechanic perform coolant servie and change hoses clamps and t-stat. Labor to change t-stat was over 3.5 hours due to its location and the fact that exhaust components had to be removed to get at it. After driving vehicle 5 minutes, the 'service engine soon' light came on. I don't know what the code is yet, but I sure hope it is a minor issue.

Any guesses as to why coolant servicing would cause a code to appear?

[dewaynep]

Could have left a sensor or 2 unplugged?

[danielsatur]

I wouldn't guess yet! ,the P-code will tell you what sensor was forgotten.