2004 2.4i starter or ignition switch?
 

So today, i was driving a majority of the afternoon. i get home, get ready for work and i go out and leave again for work. i was almost low on gas but i was on the way to refill until, while i was driving, my engine just shut off and all of the lights turned on. it was confusing because ive had power surges in my car whenever my battery terminals were loose but id solved that issue sometime ago. i go to park on the side of the road and continue to try and turn my car on but all i hear is a grinding sound coming from the middle of the engine (what i assumed was the starter). all the lights were still functioning and i kept trying and trying but it would just continue to make the sort of grinding/whirring sound. after a few more times i noticed the lights dimming a bit more so i just waited for the tow truck to come and take the car back to my house. battery is probably losing some juice now but im still baffled at what could’ve caused my engine to just shut off like that. did some digging, an ignition switch sounds reasonable bc im some other forums, apparently the starter couldn’t cause a moving car to to cut off the engine. then again, somebody said they replaced their starter and it was the issue. so im confused and if anybody could help, id much appreciate it!!!

- omar

It all kind of depends on which lights came on and the noise you're hearing. Generally, with modern computer-based vehicles the computers start losing their minds if the battery voltage drops (like if you have a bad alternator, and possibly a bad connection to the battery, as you mentioned). If the starter motor was engaged and actually turning over the engine normally, that means something altogether different, but it's hard to know from your description - the "grinding" sounds ominous, but the "whirring" sounds like a starter without enough juice to engage fully (the starter motor could spin without the Bendix gear engaging with the engine's flywheel).

If it starts up normally after being charged up, check the voltage - if it's much less than 14 volts with the engine running, there's a problem with the alternator or the wiring. Voltmeters are dirt cheap (you can get a free one from Harbor Freight occasionally, for example), or you can get a little voltmeter that plugs into the cig lighter plug for a few bucks - a great, cheap easy diagnostic tool.

back again with the same issue.
 

So i’m having the same issue with my s40 from my last post. i had a friend of mine come n check it out and was telling me it’s my alternator and my battery. i ordered an ignition switch earlier this week just in case it could’ve been the issue and nothing. so earlier i managed to buy one at my local oreilly’s for about $380 (ridiculous i know). before he installed it, he noticed the ac serpentine belt was gone. thinking that was the issue with the car i bought a new one and replaced it. the battery at this point was dead so we figured we’d charge it up. after a few minutes it still wouldn’t crank. it would make a few slow clicking sounds and that’s about it. so we came to the conclusion that it’s the battery. i return the alternator and buy a new battery. a whole lot cheaper by the way. i install it in the car and everything seemed to have livened up a bit more. the “immobilizer see manual” light turned off, which i thought was a good sign. everything seemed good until i tried turning it on again ad the same whirring sound that happened initially continued, and continued... and continued. no crank no nothing. at this point i wanna give up but obviously im not. i just wanna fix this damn car. PLEASE HELP!!!

Have you checked the voltage with the car running? Can't help you if you don't give us any info...