I will try to make this short. A week or two ago, I got a frantic call while away from home. A warning light that looked like this:
(( ! )) came on. It looked similar to this: ( ! ). The first is the brake light warning and the second is the low tire air pressure. After a few days and several hours I found out that:
1. The dealership did not know what the parameters for setting off the warning light were.
2. Incorrectly identified the wheel (tire) causing the warning light to illuminate
3. Told a story (lied) about which tire was the cause, did not check the spare and did not know that the spare could indeed cause the warning light to illuminate
The answers are: 5 psi difference between the highest and lowest pressure readings will cause a warning and that includes any of the five wheels (tires). The sensors are in the wheels themselves. The dealership reported 32 psi all around. The actual pressures were: 30, 30, 30, and 33. I took the car, a Toyota Highlander Limited V6 to another automotive location and they discovered that the pressure in the spare was: 28 psi. Ah Ha!! 33-28=5 !
All this was understood because I went to school when Math was taught as a discipline, not as "fuzzy or "everyday math".
All these unnecessary warning lights were caused because a few drivers did not understand or were too lazy to check their air pressures in SUVs driven in the South West United States a few years ago. Now all of us must suffer this unnecessary, redundant and over simplification which turned into unknown by even dealerships that sell the product!
<---- (The gauge on the left indicates 33 pounds per square inch.)