Whenever I turn on my Yaris, and, from time to time (but now always), after I accelerate from being stopped, my engine will emit a horrible screeching sound that I’m assuming has something to do with the serpentine belt.
Now you gearheads are all saying, in your heads right now, “Just replace the belt, Homie! It’s a 15-minute job that will cost you $25, tops.” Except I (well, my mechanic) did just that, a week ago, and it’s still doing the same thing.
I figure either I bought the wrong belt (not likely), the mechanic did a half-ass job (possible), or there’s something else going on (maybe). Or perhaps there’s some oil or something - perhaps from the mechanic’s hands - on the belt and it’s slipping or something.
I had similar screeching in a unrelated vehicle - a Mitsubishi Pajero IO.
I had cleaned the intake. Flushing all that carbon crud out meant that it was trying to idle much higher than it needed to. When I took it for an oil change the mechanic turned down the idle. Screech is gone.
Maybe turning down your idle is an option for you?
the screech is coming from where the belt is sliding across one of the pulleys insted of turning it. possible cause are:
that the belt is just loose, unlikely if youve just replaced.
that there is a shiny spot on one of the pulleys that allows the belt to slip.
there is some mechanical issue with one of the components driven by the belt (ie: power steering motor) that prevents its pulley from keeping up with the belt.
in order to fix 2 or 3 youre gonna have to isolate the problem pulley and figure out why it is a problem. it may be as simple as cleaning the pulley. you may have to align or tighten the component. or you may have to repare or replace the component. if you trust your mechanic she should be able to isolate the problem for you and give you options for a solution.
TLDR: It’s apparently a common problem on Yarii and a couple of other Toyota models. The guy in the video I linked above thinks it has something to do with the computer sending a bad signal to the alternator. He says to turn the key slowly, rather than quickly, to give the computer enough time to analyze the data before it sends a signal to the alternator. Gonna run outside and try it, will be back to report my results.
This vehicle does not have a self-adjusting mechanism for the belt and thus needs to be manually adjusted. It’s a multi-ribbed belt, which needs to be much tighter than the V belts that were common years ago. It’s certainly possible that the mechanic is not very familiar with manually adjusting multi-rib belts and didn’t get it tight enough. Also, new belts can stretch and require re-adjustment.
If it makes noise with the belt properly tightened I would remove the belt and manually spin all the pulleys driven by the belt to see if there’s any sign of a problem there. A worn/dry pulley bearing could screech.
It’s possible it’s a faulty belt, and replacing it with a new one will solve the problem. This is not common, but I have seen it happen.
Its surely just an analog circuit, but its giving time to charge a capacitor. The alternator’s being isolated by a relay ?
One way to rejuvenate a belt that seems a bit shiny is to clean its surface with turps or white spirit or something similar.
The problem with that solution is now I’m going to try and fix everything that way.
Bike tire flat? Squeeze brake handle.
Front door lock sticking? Open upstairs window.
Have you thought about approaching Toyota for the cost of the new belt and repair?
Probably not going to work but, might be interesting to see their reaction.
