Yaris Brake Grinding

[Mike R]

My son has a new 2010 Yaris - and the brakes occasionally make a grinding pulsing noise and the car pulls to the left. A few moments after this happens the ABS and TRACTION indicator dashboard warning lights will come on.

The car has ABS brakes, disk brakes in the front and drum brakes in the rear.

I understand that an improperly adjusted rear drum brake can create braking imbalances (fishtailing) that could cause the ABS system to activate (hence the grinding/pulsing noise). I also understand that rear drum brakes are automatically adjusted when the brakes are applied while the vehicle is traveling in reverse. So, I went into a big open parking lot, reversed as fast as I could - then applied the brakes real hard. I did this several times - but it didn't solve the problem.

My son took the car back to the dealer because the car is till under warranty - but the dealer says there is nothing wrong with the car. This is very disconcerting. There is something wrong with these brakes.

Can anybody shed some light on this. What's wrong? How do we fix this?

Mike R