sig

I was wanting to know exactly how the TPMS works. At what pressure is it supposed to alert you and what are all the variations that the system will recognize. Like one tire can go down x psi or all tires have to go down x psi, etc.

icantdrive55

Don't count on this as 'gospel' because I'm not a Ford mechanic, but in talking with a tire dealer, he said most systems are programmed to alert when the pressure sensor(s) detect a pressure 10% lower/higher than the factory specified pressure (presumably the pressure listed on the decal on the driver's door post). Since each tire has it's own sensor, the alert could be based on one or multiple wheel pressures being out of range.

gmm

The Ford dealer that I bought my new truck from last week said that it only takes about a 1 Lb. drop in air pressure to set the sensor alarm system off on any of the four tires. He said this has been the most complains that new truck buyers have told him about.

sig

Well I was asking because I tested it the other day and I deflated my driver side rear tire to 20psi before the light came on. I keep my pressure at 40psi all the way around. I wanted to know for sure if that was a problem before I took it in to the dealership for them to look at.

I did not try to drop all the tiers at the same time to see the result on that.

Sturgisfdb

Before the 09 F-150 i owned a 05 Mountaineer. I noticed the warning would come on when the pressure went below 25 psi. One tire will set the warning off, but it's up to you to figure out which. It would be nice if the monitoring system could tell you which tire is low. I live in the northern states where it gets pretty cold. It's not unusual for the tire pressure to drop significantly in the winter months.

techrep

iTrader: (1)

I believe the info is on the label on the driver side door...

Platinum_Sean

The transmitters in the wheel, transmit only when the tire is in motion. It is possible that at 30 PSI the light would have come on, if for example, you lowered it to that, and took the truck for a short run.

My 07 Caliber actually shows the pressure in each wheel, in real time. Kinda neat to see how the tires change pressure on only 1 side, on a warm day for example (the sunny side of the highway).

Remember- always check your pressure when the tires are COLD. 40 psi, in my opinion, is a bit too high (assuming its a standard tire, with a nominal 36 psi being mentioned). You in effect reduce the contact patch with the road as the pressure increases, thus reducing optimum traction for braking/take-off.

S

techrep

iTrader: (1)

Don't know about the higher pressure...I run 50 PSI in my tires...TPMS never comes on.

Sturgisfdb

I don't think the tire has to be in motion for the sensor to transmit. I have started my truck in the drive way on cold mornings, and the warning would come on. Drive it several miles to the gas station to add air, and the warning light would go off after the tire warmed up. The 09 might be different, but i wouldn't know why.

Platinum_Sean

Yup- this is how the batteries in the transmitters last so long. When they stop moving, they go into a sleep mode, and do not monitor or transmit anything. Once they rotate, they wake up and do their job. If the eraly morning pressure reads high, or low, go for a drive to "wake" up the devices and see if the warning goes away.

S