No. Codes are stored on non-volatile memory and clearing them requires a suitable fault code reader/scanner or computer with diagnostic software. On some vehicles yes, others no.
You must repair the problem or the check engine light will just come back on immediately. On some vehicles disconnecting the negative battery cable for 5 minutes will reset the light.
First you need to repair the problem or the light will just come back on. The charge varies greatly from place to place. Try disconnecting the battery for 1 hour which works on some vehicles.
None, other than the battery will loose some charge unless you connect it to a battery tender.
In the engine compartment , on the drivers side , by the brake fluid reservoir ( Ford recommends disconnecting your battery cables before servicing anything in the PD BOX , although some people have problems BESIDES resetting the preset radio stations and relearning the idle after disconnecting the battery cables )
I am not sure why but some vehicles will not permit key removal if the battery is dead
Generally when a car battery does not keep a charge it means that the battery is shot or that you will need to replace the alternator. You can check this by either taking it to your local parts supplier. For example: Advance Auto Parts or Auto zone which can both test your battery easily and there is usually no to little charge for this service. On the other hand you can do this youself by simply starting your vehicle and disconnecting your battery from the positive side, if the vehicle stalls out tis generally means that you alternator is either shot or on its way out. If the vehicles continues to run, Your battery is dead. Simple way to check on some vehicles if you have dual batteries, for example on larger trucks, take it to one of the places listed above and have them check it quickly
Precaution means to be careful, take preventative measure. Some more well used synonyms for precaution are care, safety measure, wariness, caution and discretion.
No, except on some vehicles you must enter a code in the radio in order for it to work.
Some vehicles such as older Hondas have a place to use your key to unlock the shifter. If there is none then you will need to replace the battery, or connect a charger to the battery, or jump it from another vehicle.
Before you reset (erase all stored trouble codes) have the OBDII system scanned and the trouble codes retrieved. Resetting can be done with the OBDII scan tool, or by disconnecting the NEGATIVE battery cable for a couiple of minutes. Disconnecting the cable on some vehicles causes other performance codes to also be erased and the vehicle may run rough for a few miles until the computer "re-learns" the settings.
Are you referring to the Check Engine Light? If so, you can try disconnecting the positive battery cable for 30 minutes. This will reset the light on pre-OBD2 vehicles and some early OBD2 vehicles. If that does not work then the only way is to use an OBD2 scan tool. Of course if you do not repair the problem that caused the light to come on in the first place, it will just come back on again.