Hi, on most newer than 2000 vehicles, there is a computer cut out to the starter solenoid performed by the security system or theft deterrent system. also the pcm(powertrain control module) or engine computer does have an ignition sense circuit designed to control various functions. perhaps the ignition switch could be causing the problem, bad connection could be the case there. if the theft deterrent system is causing it, the security lamp may or may not illuminate. it maybe stored in the pcm memeory diagnostic codes only. you may want to take to repair shop. .... one more thing to check, if your key has a diode in it(looks like a black chip with a wire through it) check it closely to make sure it is not dirty or wet, or any other contamination of it. the diode is of specific ohms value and if any of the above mentioned things occur to the key, it will lock out the security system. good luck.