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Hello, my name is Bobby. Thank you for the question. The most common cause of your vehicle acting like this is a failing crank position sensor. If the crank sensor is not reading right then the computer will not be able to properly send fuel and spark into the engine to keep it running. A failing fuel pump can also cause this, but the sensor is much more common on this engine. Please let me know if you need more help.
Are you getting a key or security message on the dash when you try starting it?
If you get a key start error then yes, it is more than likely the key. If the key is not sending the right signal or if the electronic ignition switch is failing and not picking it up then this will occur.
Those are the most common that I have seen but if they have checked them and if you are getting that start warning then it is more than likely the key. But, if the system is not picking up the key this will happen also. They could see this with a factory scan tool.