A steady light means the car has stored a fault and wants it read. It is not an emergency, but ignoring it costs money: the commonest cause we see is an oxygen sensor reading wrong, and a car running rich on a bad sensor will kill a catalyst, which is ten times the price.
The scan is 4,500 and comes off the bill if you have the work done here. We give you the codes, the live data that proves which one matters, and a price. Sometimes the answer is a loose fuel cap and you owe us nothing.