How low does a tire have to be to trigger sensor light?

[artfreak]

Hi
Hey everyone...Ive a new o8 yaris sedan for six weeks now, all my tires were at 26 not the recc'd 32...why didnt my tire sensor light tell me?

I think it'd been that way for a time too (not just today) I did see what looked lower but kept thinking the sensors would tell me (was trying not to be a worry wart for once)

I finally used the gauge to check and duh they were low.

I hope I didnt damage anything anyway....whats it take for the light to talk to me?

Is it that undependable or is it more for nails in tires? I really dont want to have to do the whole dealer thing if I dont have too.
(and yes I will check from now on Ive never had sensors before didnt have the hang of it yet)
Thanks!

PS: should i be glad its quiet and shut up LOL? Ive read other posts and they sound pesky (sensors).

[Diesel_Clatter]

I'm not sure what kind of tire pressure sensor your Yaris has but I think some of them work by using the ABS sensor to see if one of the wheels is turning at a significantly different speed than the others. For this to happen because of tire pressure one of the tires has to be significantly lower in pressure than the rest. If they are all equally low the system can't tell that anything is wrong.

[artfreak]

Well I dont have abs brakes but your reply makes sense and its prob' same reason more or less for our yaris. Since all four had even loss.
Thats the normal way for healthy air loss I think always was on prev' cars.

I will go back to my checking things sched from past. And hope the sensors talk to me if I have a nail or something.

Thanks

[eastbeargts]

browse through your owners manual, theres a ton of info in there that you should know. the yaris does run off of the abs sensors (as many toyotas do). i also believe that the difference in pressure has to be around 12 psi (indicating that one of the tires is flat) if they all drop at the same rate, all the tires turn at the same speed anyways. there might be some sort of 'back-up' system through rpm/gear/speedo inputs....though i have no actual data for that, just throwin it out as a maybe...

[artfreak]

I appreciate your input I dont have abs brakes tho', I did thoroughly read the manual Im anal about such things LOL. There really isnt much in it about the sensors, maybe w/ the basic models they dont inc much I dont know.

Wow 12psi loss geez if I dont catch it by then Id be driving on my rims LOL!

I do appreciate the info thanks again.

[Dake]

Sorry for the necro post, but it seemed to go along with this general theme. We just had the tire light come on on our '08 Yaris and I checked the pressure and all four tires were good and within 1 lb of one another.

I even tried disconnecting the battery, but as soon as I started it up after reconnecting, the light came right on and stayed on again. Any ideas?

Edited to add:

Ok, I answered my own question. Apparently there is a Technical Service Bulletin out for this very item.

Edited again 4/28:

Yep, looks like one of the sensors wasn't working properly so they swapped it out and now I'm good to go.