Depends on why the light was set. If its not a hard code it may reset itself after so many consecutive turns of the ignition where the code is not set again. If it has OBD 1 or OBD 2 you can get a cheapo code reader from a parts store and pull the code and fix the problem and code might go away on its own or most code readers can clear codes as well.
NELSON
check your fuse box. That fuse might have short circuit
Yes, idling in park.
ambient/battery temp sensor hi
It is... 31- Bad Evapotator purge solenoid circuit or driver
You should check your fluid levels, your oil and coolant.
Trouble code P0171 means:System too lean (Bank 1)
Code 7 2 is catalytic converter efficiency below required level
Check the coil pack or the cam position sensor
Check the engine ground before replacing parts. I have a 97 Plymouth Breeze that would not turn over, but the lights and radio worked. After replacing 4 parts (starter/solenoid, ignition switch, crank case sensor and safety switch), it turned out that the engine was not grounded properly. Once the ground was reattached correctly, car started.
check your water...
Check for fuel Check for spark
Have electronic vehicle speed sensor in transmission checked out. It will cause loss of speedometer function and set a fault code(check engine light).