I've got this 2001 Monte Carlo SS, I bought it for 3k and it only has 100k miles. But yet it quit about two years ago. I don't know what the problem is. I tried describing it in the video. But I don't know what it could be, it's not a dead battery or a bad starter. Both have been tested. The OBD scanner only shows a cooling fan error. The engine won't make a full revolution. About halfway through making one revolution, the engine/flywheel locks up. Making it unable to turn the engine further. By hand or starter. What could it be? I heard it could be a faulty transmission. The engine by the way is a gm 3800 series II 3.8L V6. (I've been struggling to attach the video so here's the link to it on youtube):

 

I have never heard of a transmission causing a no-start (not saying it can't, just not something I have heard of). You mentioned that you or someone attempted to rotate the engine by hand (I assume socket on the bolt for the crank and then using a ratchet/breaker bar and moving it). The fact you said "it moves" but then stops is interesting. I believe due to the compression in the cylinders, it will reach a point to be hard to keep rotating. To prove that, you can remove the spark plugs on all cylinders (this prevents the cylinder from holding compression to fight against).

Have you validated the battery is good? Even if it has 12v, it might still have a problem (not enough amps anymore to work the starter). Any other information you know about it? Any messages on the dash like "security"?

 

There was also a time when I was turning the engine counterclockwise (like a fool of me) and I heard something drop into the oil paint or tranny pan, took the tranny pan off, and nothing to see, and as we all know it is a pain to get the oil pan off on these new gen MCs. The noise of something dropped sounded like something falling to the bottom of the pan, I wouldn't know though but it could be something interesting. The engine makes a full revolution going counter-clockwise but not clockwise.

 

The transmission shouldn't be able to lock up the engine. They're connected by the torque converter which is a fluid coupling (i.e. would spin freely when turned slowly) unless the converter completely came apart inside which is unlikely.

When you say turning "by hand", you mean a socket + wrench on the crank bolt, right?

If its locked up so tight you can't turn it with a wrench, then I don't think you've got an option but to start pulling things apart. Probably worth a try to pop the spark plugs to make it easier to turn, but if you've got a wrench long enough to grab + turn on that crank bolt, you should have more than enough leverage to turn the engine over with the plugs in.

I'd probably pull the heads first to look at valve train, then the front cover to see if something got jammed on the chain (maybe the tensioner broke and wedged itself in there). If still nothing, then pop the rest of the engine out.


Edit- Thinking about it more- Id actually probably start with the flexplate. Pop the inspection cover off the bottom and stick a light + mirror or a snake cam up there to see if its cracked near the center. Ive never personally seen one break so bad that it locked the engine, but its certainly not impossible depending how it chunked out. They're also pretty common to crack.

 

The biggest thing that has me is the statement "full revolution going counter-clockwise but not clockwise". Tells me the engine is NOT seized since it moves. But suggests Bumpin' might be on to an idea with something came apart and is "jamming" so it only moves in one direction.

You mention that you thought you heard something fall in the oil pan. Not sure what that might be. Plus there is little direct travel to the oil pan internally. I forget the term, but the pan gasket has a lot of coverage over the oil pan. But thinking about Bumpin's comments, maybe something with the timing chain came apart and that is the sound you heard.

This is a difficult situation. It might require some clever inspecting and possibly some taking things apart. If you are not comfortable with that, might be worth contacting a reputable shop.

 

So I've worked on the car since I've last been here, I took off the timing cover, and the timing is good. I've come to realize it's something interfering. Because as I turn the engine with a rachet & socket, I hear a clunk-like metal-to-metal contact. Now I'm in the process of getting the oil pan off because I remember something dropping down into there and when I shake it around ( I already got it loose) I hear and feel metal moving around in there, Once I get it off I'll let you know what it is, but so far it does not sound good and the engine might have to come out :'(