Yellow exclamation Warning Lights

(_!_) = One of your tires is low. Check around your car to make sure one of your tires isn't low. When you find the one that is, put air in it, and get it fixed soon!

 

The yellow exclamation is the brake control warning light. It may go away on its own after a few restarts. If not, it may indicate a potentially serious issue. The wisest course is to visit a shop (dealer or independent Toyota specialist) to get that code read.

 

I Thinks it's the low tire warning.

 

There are unfortunately two warning lights that look similar. kohnen's (_!_), where the _ are really squiggles like ~, would be for low tire and/or other problems with the tire pressure monitoring system. The brake system warning is also yellow and looks like ((!)).

 

I had this happen this morning. It was unusually cold and within a few minutes, it shut off. I will check my tires to make sure one isn't leaking but does anyone think the cold morning could have something to do with it?

 

Tire pressure goes down in cold weather. Sadly, air never leaks into tires.

 

That is sad.

 

To be pedantic, air does leak into tires, but it leaks out at a faster rate.

Tom

 

Really? I always thought the rate of leakage was a function of the pressure difference across the void through which leakage is occurring.

That being so, the internal pressure would need to be less than the external pressure for inward leakage to occur!

 

The rate of leakage *is* a function of the pressure difference across whatever membrane or void is in question. That part you have right. What is confusing you is that the rate of leakage is the net result of molecules leaking in and molecules leaking out. Think of it like a shopping mall where some people are walking in and some are walking out. Both happen at the same time, but if more walk in than walk out, you end up with a higher density of people inside.

Air in tires is essentially an ideal gas. As such, the gas molecules bounce around randomly with very little interaction. Molecules inside the tire occasionally find microscopic holes and escape. Likewise molecules outside the tire also occasionally find the same holes and sneak in. If the tire pressure is the same as the outside (a flat tire), just as many molecules sneak in as escape. The tire neither inflates or gets any flatter. The molecules are going in and out, but the net result is zero change.

Now if we increase the pressure inside of the tire, we have more molecules zipping around. More molecules means more of them will find holes and sneak out, so the net result will be a loss of pressure. Molecules are still finding their way into the tire, but more find their way out.

In case you are interested, this is why you can smell a fart upwind.

Tom