Hyundai Repair: sonata no start, crank sensor, autozone

Question
My 2003 Sonata V6 has an intermittent starting problem. It cranks fine but at times wont start. I tried resetting the alarm and it appeared to start when i adjusted the sunroof. Also the alarm was setting on its own after 30 secs or so if I am in the car with the ignition off. Do I have a bad immobilizer or alarm unit?

Answer
Depending on the circumstances, it's possible your alarm unit is working normally.  Anytime you use the remote to unlock the doors, the electronic time and alarm control module (ETACM) waits 30 seconds for the driver's door to open.  If the driver's door doesn't open within 30 seconds, the system presumes that the unlock command was received in error and then relocks the doors and arms the alarm.  If the alarm is inhibiting starting the car, it'll prevent the starter motor from turning, so we know this isn't an alarm problem.  Also, presuming you have a U.S. vehicle, you don't have immobilizer.

Chances are good that the seeming relationship between operating the sunroof and vehicle starting is nothing more than coincidence.  There's nothing shared between the two circuits.

The majority of crank-no start issues are either problems with the crank sensor or fuel pump.  If you can, the next step is to try to determine whether you have spark and fuel pressure when the problem occurs.  Lack of spark is usually caused by a faulty crank sensor, and lack of fuel is often caused by a faulty fuel pump.  A faulty crank sensor usually sets a trouble code even if the check engine lamp doesn't come on, so it may be a good idea to stop by AutoZone or AAMCO and have them scan your ECM for codes.  Also, don't be fooled into thinking that lack of fuel pressure necessarily indicates the problem is the fuel pump.  The problem could be with the power or ground circuit for the fuel pump as well.