A warning light showing a yellow circle with a triangle and an exclamation mark came on this morning, and stayed on for the 4 miles or so I drove to work. What is it? What should I do about it. For your information, it was, and still is, cold today in Minneapolis. Around minus 20 deg F. Would that have anything to do with the light coming on?
The triangle with the exclamation mark inside, and the circular arrow around it, is the warning indicator symbol for the Electronic Stability Program (ESP). It should illuminate when you turn the key and extinguish after about 2 seconds after starting.
The ESP as well as the ABS system are intertwined. ESP uses the ABS to correct various safety/handling concerns by applying or releasing pressure to any particular wheel or wheels to help stabilize the vehicle. It can also, override throttle input if it is appropriate. An example would be if you had to swerve hard to avoid a collision at high speed. If the car were to begin to slide, be it understeer (front) or oversteer (rear) the ESP would adjust throttle and wheel speeds to stabilize the vehicle. Quite amazing actually. Also, if you accelerate too quickly on ice it will adjust wheel speeds and the light will flash. This indicates the system is in "control mode".
As with ABS, it is supplemental and only comes into play when it is needed. If the MIL (Malfunction Indicator Light) is illuminated consider the system inoperative. The ESP controller must be scanned with a factory capable scanner for the Trouble Code Fault to determine the cause of the MIL illumination and testing of the effected component/circuit.
When you start the engine, if the light remains illuminated after starting, you can Try to reactivate the system by shutting the vehicle off, and then restarting it. Also, there should be a ESP switch on your center console that turns the system off and on. Possibly you pressed this switch by mistake? The system can be shut off for special reasons explained in your owners manual under "Electronic Stability Program".
I hope that I have answered your questions and addressed your concerns. Should you have any further questions for me, please do not hesitate to ask.