failed em test says NOT READY then drove it n check engine came on smell burning on 1999 Chrysler Concorde

smell burning lik overheating every so often but not consistent and check engine light popped up as soon as i put 80 miles on it after failing a emission test due to system not ready beacuse i changed the battery

1 answer
scan codes and post so we can adv it may be a thermostat issue