Battery Light Illuminated

Ok, so I was advised to replace my serpentine belt due to it having cracks in it. I replaced it, the belt I replaced it with was the exact spec 975 6 rib however the product code was 6PK975 and the one I took off the car (original) was 6PK976. Could this be the reason why? asking before I get the right belt tomorrow and change it.

If the replacement belt is a half inch or inch longer, I suppose it would be possible that the alternator is slipping under load. Maybe someone can check the specs on the two belts. Always helps to double check part numbers.

I checked the part numbers before replacing both are 6 rib 975mm long however the original has a product code of 6pk976 I’m assuming that in reality its a mm longer? the car drives normal I did around a 70 mile journey in it and it didnt break down and battery still isn’t dead

Yes the one is a mm longer. 975 vs 976. Don’t know if that’s enough to make a difference or not but it was on my lawn mower. Use a voltmeter to check alternator output and battery voltage at rest.

Well since we don’t know the year make model and engine size, we don’t know if it has an auto tensioner or not…

If your battery light is on then you need to see what the charging voltage is… You could have bumped the plug on the alt knocking it loose or any number of things…

Is it squealing/chirping any now, is the power steering harder now?? (could have electric but we don’t know what you are driving)


When you went and purchased the new belt, what did you tell the counter person to make sure you got the correct belt?


From here it looks to me like you put the belt on wrong and are driving the alternator backwards.

Fiesta 1.6 TDCI

its an auto tensioner also no squeeks or noises

is that even possible?

I’m pretty sure he was being sarcastic being as you gave 0 details about the Year make and model of the vehicle you are working on at the time he posted it…

Yes, it is possible, and not that uncommon of a diy’er mistake, on certain engines. When replacing belts, good idea take a photo and make a sketch of the routing before removing the old belt . Suggest to get the standard shop battery/charging system test. My diy’er version, before first start of the day battery should measure about 12.6 volts; then immediately after starting engine, 13.5 to 15.5 volts.

As far as whether that’s the correct belt for the car/engine, no idea. When purchasing parts, suggest to hand the parts staff paperwork showing your car’s make/model/year/configuration and VIN. It’s often possible for the parts staff to just type the VIN into their computer and get the correct replacement part number. You might surf over to the Gates website; they may have some info there on their belt applications, which engine the belt is designed for. And there’s always the dealership; somebody there – if you can find them – they would know for certain. If the only difference is 1 mm length, seems pretty unlikely to cause alternator problem.

The crankshaft turns clockwise, the belt rotates in a clockwise direction, how does the alternator pulley rotate counter-clockwise?

Plus some of the alternators have a one way clutch pulley, so they don’t spin backwards by the pulley…
Clutch pulleys, also known as one-way or decoupler pulleys, are designed to decouple the Alternator from the rotational forces of the engine crankshaft pulley and serpentine belt

You would need V groves on both sides of the drive belt to route the belt in that way, only Volkswagen uses belts of that type. You say this is not uncommon?

Plus most alt are on the outer side of the engine which means the belt could not be placed on it wrong, routing the belt on the wrong side of a pulley is more common on more inner pulleys like idler, W/P and or tensioners…

Using your diagram as an example, the very bottom pulley would be the crank, the one just above it would be a W/P or tensioner/idler (depending if auto tension or not) and the top would be the alt, now think about how you could ever run a belt on the wrong side of that pulley…

I have no cars w/serpentine belts, so never has been an issue for me. Common or uncommon is a judgment call . Are you saying it is simply impossible to route a non-VW serpentine belt incorrectly?Do we know the make of this poster’s car? Even for a non-VW belt, it seems like an inexperienced diy’er could get the wrong side of the belt against the pulley and not notice at first.

“Assuming it is a serpentine belt system, it is possible for the alternator to run backwards.”

Need to read the thread again…