I drive a 2006 Cobalt SS (not supercharged) with the 2.4L engine.

Today my serpentine belt broke. I need to get the car into the shop this week for a different problem. I'm fairly confident that I can get a new belt on without too much trouble, but I do have a few questions.

I got the car in late 2005/early 2006. It has almost 100,000 miles on it and the belt has never been changed, so it seems plausible that the belt was simply old and worn out.

From everything I've read so far it seems that the next most likely cause is that some pulley (either the tensioner, alternator, or compressor) has seized up, eventually resulting in the breakage of the belt.

If the problem is just the belt, no big deal. Fixed by replacing the belt. The question is how can I diagnose the other possibilities?

Also, if I find that one of the pulleys has seized up, should I attempt to drive it to the shop (about 2 miles) or should I have it towed in?

Thanks in advance!

  • The A/C Compressor locked up, causing the belt to break. I'll scan over the answers and see if any of them fit. Commented Sep 13, 2013 at 17:12

3 Answers 3


It sounds to me like it was just worn out.

You should be able to turn the alternator and a/c compressor pulleys by hand. I'd replace the tensioner if it hasn't been done already anyway, and with a new tensioner, fitting a new belt should be fairly easy* as you can fit it with the tensioner un-tensioned.

However, if the auxiliary belt hasn't been changed in 100,000 miles, chances are the cambelt (timing belt) hasn't either. If that is the case, that needs to be changed asap, as a broken cambelt can cause catastrophic engine failure - of course, if you have a timing chanin rather than a belt this isn't a problem.

As for driving it to the workshop, if the belt only drives the alternator and a/c then this should be fine, as the car will run quite happily without them for a short distance. If it also drives the water pump however then you must not drive the car without the belt fitted, as the engine will very quickly overheat.

*for given values of easy - I've seen cars that require engine mounts to be removed to change the belt as the belt passes through the mount, and other cars where it can be changed in seconds...

  • 2
    +1. Also, while the belt is off, in addition to checking for seized pulleys and tensioners, check for excessive bearing play in all of the pulleys and tensioners. Now is the time to replace them if they're on their way out.
    – mac
    Commented Aug 14, 2012 at 15:58

It's quite possible it just broke due to age and wear. I have personally experienced that when the belt wasn't replaced on schedule.

If you were in the vehicle when it broke the belt, I'd be surprised if you wouldn't have heard loud unpleasant noises or felt something if it broke due to something seizing up. If it just broke, all you would have noticed was a muffled thump and the illumination of the warning light to let you know your alternator voltage just went to zero.

You can see if you can move the tensioner to verify it's not seized. You might need a lever. A socket wrench will sometimes work, or you can rent a tool from a parts store.

As for the rest of the pulleys, maybe you can move the ac clutch or the water pump or alternator by hand, but I don't think you're going to get the hub attached to the crankshaft to move.

So, you might poke around bit before replacing the belt, then watch it when the vehicle starts. Should be easy to spot a seized pulley, but it might also be a good way to catch a broken belt in the face, so don't watch too close.

If one of the pulleys is seized, I don't see how you're going to drive it to the shop, unless it's the belt tensioner, and if it's that one, I'd be surprised if you could the new belt on, depending on what position it's stuck in.

I don't think you want to drive the thing without the belt on, I think the water pump is belt driven. Check the belt routing diagram. Should be on the underside of the hood or on the radiator support.


You can change them pulleys yourself. The idler pulley kept tearing up my belt. I found out that changing the idler pulley change the tention pulley too. All 3 items should be less than 60.00 The tention pulley gets worn causing the other to throw the belt off.

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