Since I put on new wheels with snow tires on, I noticed that my TPMS light will come on (I didn't buy the sensors). BUT, it takes it a good 10 to 15 minutes after starting the car each time before it starts blinking. At first I thought Tire Rack had screwed up and given me free sensors! :p But I'm wondering, if it takes 10-15 minutes for it to register that there is NO tire pressure, how useful would it be in the case of a fairly fast leak on the highway when the sensors are actually there? The tire could be dead flat before it even started blinking in 10 or 15 minutes. Seems this would only be useful for someone absent-minded who doesn't notice a very slow leak and never bothers to check the pressure themselves. Or is my car strange? Does everyone elses start blinking right away if they don't have the sensors in their wheels?

 

I think the difference is having no signal at all and the PCM "retrying" and finally giving up and giving you the warning light as opposed to having a constant signal and it waiting to get above or below its threshold before telling you.

Example: Say your pressure is borderline and it's cold morning (which exacerbates low pressure), as soon as it turn the car on or just minute after I'll get a warning. If I run the tires for awhile the light goes away as they warm up. I'll go to gas station and notice my pressure is near that threshold (I give it a little extra air and all is good the next morning).