I believe, traction control means you have 4-wheel disk brakes, but I could be wrong. So, I'm going under that assumption. If that's wrong, I have slightly different advice.
If the traction control light blinks, and the brakes grab, that means the system thinks there's slippage happening. I'd start with the free/easy action. Make sure the tires are properly inflated and then re-calibrate the tire pressure system on flat, level ground. I don't know if the Sienna's traction control takes that into account, but I know some vehicles do. Assuming that doesn't fix it, I will say that it's likely a wheel speed sensor that's bad. It's possible that there's a partial short in one of the wires or some corrosion on a connector. Unfortunately, I don't know if there's any test procedure for an intermittent issue which occurs in semi-arbitrary, inconsistent situations. If throwing parts at the problem is something you're interested in doing, the sensors look like they aren't super expensive. That said, I would probably consider a few general items like flushing/bleeding the brakes and lubricating the caliper slide pins. Usually, if a caliper is grabbing, you can tell which one because the brake pad will be slightly more worn on that side. If it's not the sensors and it's not a sticking caliper and it's not fixed by brake fluid, it's probably something central to the ABS system. In that case, I would actually probably advise taking it to a dealer to do a full diagnostic on the car.
If the traction control light blinks, and the brakes grab, that means the system thinks there's slippage happening. I'd start with the free/easy action. Make sure the tires are properly inflated and then re-calibrate the tire pressure system on flat, level ground. I don't know if the Sienna's traction control takes that into account, but I know some vehicles do. Assuming that doesn't fix it, I will say that it's likely a wheel speed sensor that's bad. It's possible that there's a partial short in one of the wires or some corrosion on a connector. Unfortunately, I don't know if there's any test procedure for an intermittent issue which occurs in semi-arbitrary, inconsistent situations. If throwing parts at the problem is something you're interested in doing, the sensors look like they aren't super expensive. That said, I would probably consider a few general items like flushing/bleeding the brakes and lubricating the caliper slide pins. Usually, if a caliper is grabbing, you can tell which one because the brake pad will be slightly more worn on that side. If it's not the sensors and it's not a sticking caliper and it's not fixed by brake fluid, it's probably something central to the ABS system. In that case, I would actually probably advise taking it to a dealer to do a full diagnostic on the car.
