TPMS oddity

[rawhog]

So this morning after I pulled out of the driveway, I noticed a tire pressure warning light. I pulled back in and grabbed my air hose to add some air to the tires. They wer all sitting at about 38-30 psig. I started adding air. Mind you, I had left the car "running" and the lights on while doing this. As soon as my pressure gauge hit 36 psig, the front fender turn signal lights blinked. It did that as I reinflated each tire. Pretty cool!

 

[TonyWilliams]

So this morning after I pulled out of the driveway, I noticed a tire pressure warning light. I pulled back in and grabbed my air hose to add some air to the tires. They wer all sitting at about 38-30 psig. I started adding air. Mind you, I had left the car "running" and the lights on while doing this. As soon as my pressure gauge hit 36 psig, the front fender turn signal lights blinked. It did that as I reinflated each tire. Pretty cool!

The tires were at 28-30 ?

I thought it took several minutes to update, and the wheels had to be turning (otherwise, it's saving battery in the TPMS by not updating when not moving).

Interesting.

 

[TomT]

I believe that a sudden change in pressure also wakes up the sensors...

I thought it took several minutes to update, and the wheels had to be turning (otherwise, it's saving battery in the TPMS by not updating when not moving).
Interesting.

 

[redLEAF]

I believe that a sudden change in pressure also wakes up the sensors...

I thought it took several minutes to update, and the wheels had to be turning (otherwise, it's saving battery in the TPMS by not updating when not moving).
Interesting.

I have three cars with different TPMS and can attest that sudden changes in temps drive these things nuts ... on two occasions while on a long trip from moderate to cold temps had to pull over when one tire set the thing off; in one case we needed to take the car all the way back home and switch vehicles due to the fact that one tire would not hold it's pressure. These are mandated safety related devices that do work but the reality I've found is that the quality/construction of them leaves a lot to be desired (as well as the replacement cost, where we've seen those used on the LEAF run $100 or more for EACH tire!). The ones used by Mazda are OK but not great (car that we needed to return home with --- TPMS was about $30 per tire), those on smart cars can break off easily (those ran about $28) and those on my VW/Dodge Routan minivan are just extremely sensitive but appear to be a bit better constructed. I also have a '99 Miata of course w/o TPMS and the tire valves have lasted for years until it comes time to change the tires when we replace just in case; wheels typically all stay at pressure and never had a flat. What's interesting in all this is that for all three of the cars I have it just indicates a fault and not what tire is low -- I don't have my LEAF yet so assume this is similar (i.e., no read outs from the tires)?

 

[rawhog]

Correct. There is just an icon that looks like a cross section of a tire with an exclamation mark in the middle. But, the blinking lights thing was what was cool about the whole thing. Had I known it did that, I could have done it in the dark instead of turning on my driveway Klieg lights

 

[kmp647]

the flashing lights and beep are a feature on the car call easy fill I think

helps you get to the right pressure with only a hose

beeps and flashes when you hit 36psi

 

[thankyouOB]

if all the tires look inflated, but the warning light is on--
how do I tell which tire is low and causing the warning to activate?

 

[DaveinOlyWA]

any way to change the pressure. i do 40 winter/ 45 summer on mine

 

[garygid]

Flashes lights about 36 psi, but beeps the horn
a bit later (at a higher pressure?), I believe.

 

[derkraut]

if all the tires look inflated, but the warning light is on--
how do I tell which tire is low and causing the warning to activate?

Tire pressure gauge? I always carry one; and they're only a coupla bucks.

 

[Levenkay]

Apologies for piling on, but the thread subject kind of asks for it...

Right around Thanksgiving, I bought a set of snow tires for my LEAF and had them mounted on their own rims. I'm not at all fond of the notion of $100/wheel government-mandated TMPSes, so I declined the tire shop's offer to have any of them installed in the snow wheels. A few weeks back, the weather forecasters thought we were in for a significant accumulation of snow (perhaps a couple inches!), so I decided to switch over to the snow wheels. I was prepared for some sort of pilotless State Security air-bot to come whizzing up and berate me over loudspeaker, or at least to see some flashing LED fireworks on the instrument panel due to the un-TPSed wheels, but.. nothing. I drove a few miles and back to a grocery store (after seeing to the car's mobility, the next priority was to make sure I had enough potato chips to tide me through the projected civilization-crippling blizzard) and no warning lights to be seen. Same story the next day on my 20-mile roundtrip commute: no warning indications on the dash at all. It was only on the day after THAT that I got the flashing stink-eye I'd been expecting. So I have a fair number of "idle curiosity" questions stacked up concerning the TPMS feature, and this seems as good a time/place as any to air them out:

Is it normal for the system to take two or three days (and about 25+ miles of driving) to notice the total lack of any pressure information received from the tires?

If so, of what use is the system to anyone except its manufacturer?

Or, if it's NOT normal for things to take so long, was the car's computer making a clever inference about the particular sequence of sensor readings? I mean, having all four sensors instantly (so far as the computer can tell) go from "in-spec" to "completely absent" might be taken as a clue that "maybe the owner is a cheapskate and swapped off all the wheels, so no point generating a low pressure false alarm". I kind of doubt it, because that would be a lot more sophisticated than the other bits of the car's user interface. But if it had made the clever inference, why'd it change its mind and go back to lighting up the "tire fault" warning?

I went looking through the owner's manual and the dashboard control screen for information pertaining to the tire status. It sure seems to me that if you've caved in to pressure from some government bureau and added several hundred dollars' worth of sensor electronics to the car for detecting any single one of its tires being at the wrong pressure, you'd at least want to present the sensor readings in some sort of system status screen somewhere. For Babbage's sake, wouldn't it be helpful to at least indicate WHICH tire(s) need looking at when they fault??? Is there such a status screen somewhere I didn't find (maybe it's filed under "Phone settings" or something...)??

 

[thankyouOB]

if all the tires look inflated, but the warning light is on--
how do I tell which tire is low and causing the warning to activate?

Tire pressure gauge? I always carry one; and they're only a coupla bucks.

yup. and thanks.
i was really asking if the car IDs which tire is low.

 

[anlson]

Is it normal for the system to take two or three days (and about 25+ miles of driving) to notice the total lack of any pressure information received from the tires?

I just changed my tires over from winter to all-season (both sets have TPMS sensors). I had the same experience; it took 3 days for the TPMS system to register an error. Seems I now need to see my dealer for re-programming.

It does seem odd that it takes the system so long to register an error. I guess that's to prevent false errors (apparently, 2 days without hearing from the wheel sensors is just fine...). I'm assuming that when the system is working, it will report quite quickly if a tire is underinflated.

I'm also a little miffed that one of the worlds smartest cars has absolutely no status screen for the TPMS system. That, and the 2 unsynchronized clocks.