Both drive belts just fell off

Both drive belts just fell off and I wasn’t even going anywhere on a 2011 Gen 3.

Is this a Jimny thing? I have never had a problem with a drive belt on any car in 35 years of motoring it’s bizarre.

Okay here is what happened, I was fitting a home made box so I can get front and rear cameras through one input, put it in reverse, you get the rear camera, take it out of reverse and you get the front camera for about 6 seconds, plus there is a switch on the dash. To fit it meant the head unit was out and powered for some of the time, with the ignition on, but engine not running. I was probably about 2 hours max.

The head unit tends to hang near the 2w, 4w and low range switches and when the ignition was on the drive did change a couple of times and the air con button got turned on.

Near to the end of testing, the low battery voltage warning came on so I started the engine, but it didn’t go off. Thinking I might have a wiring fault I shut everything down, pulled the head unit and all was okay. I started it up again, the low battery voltage was on and my volt meter only read 11.3v. Raving the engine a little made no difference, voltage went down slightly.

I then heard a clunk and the engine stalled. On checking both drive belts had come off.

I am guessing that the belts will need replacing, if they were just slack and had increased load from the 4w drive buttons been pressed and AC on without the engine running, then starting up could that have caused it? Or is there a guide keeps the belt in place?

I am assuming there is a guide somewhere on changing the belts?

Ta

That's unlucky.
Don't think it's a Jimny thing, but you can get wobble on the crank pulley due to the rubber insert failing, this normally snaps belts.
I've just changed both of mine, easy enough but I was surprised just how tight they are with the correct preload.
I recall watching a video or two on YouTube to get the general idea and went for it. Did it with the radiator installed, a little tight but Ok in my opinion.
Mike

Edit
Here's one

Thanks Mike,

It looks straight forward, I think I will try the old ones back on tomorrow and my local parts store has Dayco belts in stock, so will swap them over, if the old ones stay on and nothing else is wrong, like a seized water pump or AC compressor.

I am working from home tomorrow so should be back up and running quickly.

At least there is no damage, just a mystery how the belts came off in the first place.

Yes it's strange, can't explain why they both came off without damage.
It's possible they were just on the loose side, but you usually hear them squeal with lights on or PAS movement.
The only common point for both is the crank pulley, so have a good look at this to make sure it's ok. Pulley should run true, wobble indicates possible issue with the rubber bonding.
Hope the fix all goes well.

Definitely check the condition of the crank pulley.

As said above its possible that the ac pulley was jammed which could have caused the belt to jump and then take the alternator belt with it but I agree it's more likely the crankshaft pulley is failing.