Help understanding TPMS

[payyourtoll]

I'm confused with whats going on with my FX. Yesterday I dropped the car off at tire place to simply have the TPMS sensors removed from my stock wheels in prep of moving them to an aftermarket set.

The guy called me and said I only had 3 sensors, the fourth wheel just had a rubber valve stem. I never noticed it had only three, but ok.

So now the TPMS dash light is on, like I assumed it would be. When I navigate on the console screen to the air pressure, all four just show **. There is no sensor in my spare.

My question is why was my low tire pressure indicator NOT on if I was missing a sensor to begin with? I want the light to go off when the new wheels are installed, so I don't understand if I now have to purchase a fourth sensor and program it? I don't get it

 

[pmanliu]

The only way I can see your tpms light not being on is if they programmed the same sensor twice to make up for the missing 4th sensor. Not sure if this is possible... But when programing sensors into my car (non Infiniti) all you do is type the serial number of the sensor in so I can see it being possible to type the same one twice.

 

[porkandbeans]

Take those 3 and make one of those pressure tubes. If no dash light for a while, the maybe somehow your car is reading 1 sensor twice. (Actually, in this case, I'd probably make 3 separate tubes and figure out what is what.)If your car only reads 3 sensors then maybe the shop lost or broke the 4th and doesn't want to admit it.

 

[shadow191]

I think the shop broke one and is lying. On the FX, they have to scan each sensor in and then plug the scanner to OBD port. There is an order to it, so you really can't just scan 1 twice.