The error code 12 refers to the blower being on after power up and, honestly, I have no idea what Carrier means.
Have you done any maintenance work or electrical work in your house. Did you get a new thermostat.
To rule out the thermostat I would go to the furnace, turn off the power and label each wire where it connects to the thermostat terminals on the control board. Now disconnect all the thermostat wires (knowing where they will reconnect to because you have them labeled). Now jumper the W and R terminals at the control board. You will be calling for heat. Now turn on the power and watch the furnace as it runs. After 5 minutes, assuming the furnace is running as you'd expect, CAREFULLY disconnect the R to W jumper you previously installed from the R terminal first. It's important to do the R terminal first. Now see if you get the same error code 12.
If you look at the back of the blower compartment door you may see the list of error codes. Otherwise Google 58wav error codes and find the site w w w dot expedio dot carrier dot com. Look for the document 58w,z(dash)5sm.pdf Go to Fig 13 on page 9.