yep thats what I assumed... Either the warning light is on or all tires pass the check. But apparently something else is causing the warning because 40psi is plenty. I dont think my tires were even low to begin with. I usually run around 35 or so but when the light came on i put them all to 40

 

The car doesn't know where each sensor is by it self it has to be programmed. A programmer would let the computer know which tire has which sensor and once that sensor would sens a low pressure it would tell you which tire it is and what the pressure is, it's just that Lexus decided not to give us that option. A lot of the American cars that have sensors including Corvette tell you which tire has what pressure.

 

BTW the light will come in if you over inflateyour tires as well..I would try putting them to the correct pressure and see if it helps..

 

The IS knows which sensor has what pressure. Lexus just choose not to display that. When you initialize the TPMS, the system records each sensors PSI, if the PSI falls below 5 PSI (or 20-25%, I forget which), the warning light comes on. If you don;t want the light to come on, let the air out of all tires to 10 PSI, re-init the system, re-inflate the tires, then light lights won't come on until you really have no air, rather than a thermal change of a few PSI.

 

It knows which sensor has what pressure but doesn't know where it's located untill it is programmed. For example if you would put a front sensor in the back of the car without reprogramming it, the car would think that the sensor is still in the front of the car. Maybe I just explained it wrong in the previous post.

 

From an engineering standpoint, the system would be significantly more complicated to know which tire location is low (front right, rear left, etc.). It would need to have 4 separate receivers that would each receive data from all 4 sensors. To determine which sensor was closest, it would have to compare signal levels for each sensor at each receiver to determine which was the strongest. Why on earth would Lexus go to all that extra effort if they weren't going to even use the results for anything? On top of that, they would have to engineer loop holes that would allow people to do the bandaide thing for aftermarket wheels that people are using now (putting all 4 sensors in a wheel barrel tire in the trunk).

 

ah... i learn something everyday...