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#41 ·
Timthom62 said:
The TPMS sensors report to the Body Control Module via RF signals. When the TPMS sensors are replaced, they have to be activated for the BCM to recognize them so that you're not getting the TPMS signals of the vehicle driving next to you. They also have to be calibrated to set their specific position on the vehicle, as each has a distinct RFID code.

The BCM compares the tire pressure received with a programmed desired tire pressure set in the BCM. The BCM is programmed with the reference pressure shown on the vehicle ID label on the drivers door sill. According to the service manual, the programmed desired reference pressure cannot be changed.

Using tires with a lower pressure would affect the accuracy of the TPMS system, and using tires below the low pressure threshold would cause a TPMS fault.
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Fun fact: The TMPS system doesn't care about which sensors are used so long as they were on the right frequency for the car once they were turned on.

I.e. if you take two sets of wheels for an MK3 Focus and swap them between cars as long as the tires are inflated properly and the sensors are functioning you will not get an error message by changing the wheels.

The car only cares that it sees four sensor addresses and gets the reading back.

The car also doesn't care where on the vehicle they are located. The only reason you'd want to retrain them after a rotation would be for locational positioning, but because the car won't display specifically which tire is at what pressure despite the sensors being capable of sending this digitized analog data to the BCM it would not alert you to which tire was low.
 
#42 · (Edited)
Well, after reading through all the posts about the TPM system in our Focus, looks like I have to buy new sensors for the winter tires I just mounted. At least, it doesn't appear that there is any other way around it. [mad]

Really sucks that you can't at least disable the system. My DD (2013 VW Passat) has the TPM triggered by the ABS sensors at each wheel, as does my SO's 2013 VW Bug Vert. Makes no difference what wheels/tires I mount on them, the TPM works. I (personally) don't need a readout for each tire - if the monitor light comes on, I'm going to check every tire anyhow. Happened once on my car already.

Figures, I buy my daughter a '13 Focus, and for a little extra peace of mind, buy a set of winter tires/wheels, and NOW I have to go buy new sensors for the aftermarket wheels. [:(]

Thank you US Gov for protecting me from myself. [doorpeek]
 
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#43 ·
OldBlue said:
Well, after reading through all the posts about the TPM system in our Focus, looks like I have to buy new sensors for the winter tires I just mounted. At least, it doesn't appear that there is any other way around it. [mad]
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I believe you can use the focccus software to change the TPMS from sensors to deflation detection system (DDS). Or you could just disable it altogether.
http://www.focusfanatics.com/forum/showthread.php?t=402666

DDS works by comparing each tire rotation - the less air in the tire, the smaller the apparent diameter and the faster it will spin. It won't tell you if all of your tires are equally low, but it should work or warn you if one tires starts losing air.

EDIT: It would still require the use of an ELM tool (not too expensive). Also, I haven't tried it myself yet to know if it even works.
 
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#44 ·
Thanks PratoN. I'll have to read through that link when I have more time. Looks like a similar way that I was able to edit the features of our VW's.
 
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#47 ·
I hate TPMs. What the hell did we do BEFORE tire pressure monitors? Oh yeah, I checked them once a week with a tire gauge! Imagine that!
 
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#51 ·
Mazdamike0831 said:
Safety first for dumb people!!!
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I disabled mine... why should I pay huge price for a set of TPMS sensors (summer/winter wheel set) because people are too lazy to check their tires????

You'd be surprised how many drivers are too lazy to check at least MONTHLY!

This should be in the driving exam yet along with the engine oil dipstick test!

/endcomplain [grinking]
 
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#52 ·
VisionPilot said:
Does anyone know what the pressure threshold is for the TPMS sensors to indicate low pressure? Does the system tell you which tire is low?
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This is from the final NHTSA rule mandating TPMS:

The NPRM proposed to require the TPMS to illuminate a low tire pressure warning telltale not more than 10 minutes after the inflation pressure in one or more of the vehicle�s tires, up to a total of four tires, is equal to or less than the pressure 25 percent below the vehicle manufacturer�s recommended cold inflation pressure or the pressure specified in the 3rd column of Table 1 of this standard for the corresponding tire type, whichever is higher (see S4.2(a)).

The table referenced is available at Federal Motor Vehicle Safety Standards; Tire Pressure Monitoring Systems; Controls and Displays

Based on a recent experience with the TPMS in my 2012 SE, it appears that Ford uses trigger limits that are higher than the NHTSA 25% value or the minimums noted in Table 1 of the TPMS standard. TPMS recently alerted me to a moderate leak in my right front tire, and the system came on when the pressure in that tire had dropped to 30 pounds.
 
#54 ·
mp223 said:
My parents' Buick lets them see each individual tire pressure through a menu in the dash while driving. Much more useful.
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This ^^^^

I hate that the Focus on displays "Low Tire Pressure" without stating the wheels that is low. Our GLK will tell you exactly the pressure at each wheel. My fathers Buick does it too.

My FJ Cruiser also only stated "Low Tire Pressure" without stating the wheels that is low. Drove me crazy for many days until I realized I need to check the spare on the back. The wide range of temps here does the pressure in sometimes.....95 on day, 39 the next night, etc...
 
#57 ·
If it was a fancier system with pressures at each, the complaints would be about accuracy, training when wheels changed, etc..

TMI & hassle instead of too little.

Few seem to like TPMS at all, Wife would drive indefinitely with the warning on not wanting to be bothered.
 
#58 ·
TPMS is great with low profile tires like on the ST.

(to beat an old horse, but I am amazed by it): Somewhere on this or another ST site was a picture of a members tire missing the entire tread area.
BUT!! The wheel was on the ground with the sidewalls still HOLDING UP the car.
(so normally the sidewall flatten out. The ST Goodyear tires have such extremely stiff sidewall they can hold up the car, even with no tread area. (the sidewalls cut through the tire and the tread rolled away separated.. on it's own.

Anyway, this means you cannot 'see' ANYTHING of low pressure in the ST Goodyear 235/40/18 tires. The only way is to check them with a tire gauge, ir TPMS to notify one.

ANd yes I agree WTF not separate notification for each tire... Cheap cheap.
 
#59 ·
I had a run flat off a bmw in like 2006. The customer complaint was hard feeling from whatever corner it was. Took off wheel saw crack in wheel. Quoted new tire and wheel. When breaking down the old one out of curiosity and to scrap the aluminum, the tire was so stiff it was still holding the rim together at the crack and had air pressure. That's freaking scary.
 
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