tpms light came on

How smart is the light, and how smart is the dealer?

(don't even ask how smart is the driver ok)

New Accord EX4 sedan about four months out of the dealer, haven't done
a thing yet but put gas in it and putter around town. Noticed the
TPMS light on, pulled over to look at the tires. Nothing obvious, so
I drove on. Next time, I looked carefully, maybe the right front was
a tad low?

Drove on down to the service station air pump, promised to buy some
gas if they'd turn on the coin-op air. Turns out that, warm, all four
tires were almost exactly 28psi. But my door panel suggests they
should be 32psi cold. Harump. I know my dealer has long had a habit
of underinflating when they adjust tires, why, I don't know. And I've
beem wondering why my MPG was a mile or two lower than on previous
Accords. Harump. So I blew them all up to about 32psi warm. Turned
the key, drove a block - light stayed on. Maybe a bad sensor, huh?

Had lunch, got back in - and now the light was off.

So, does it take a couple of samples to convince itself that the
pressure is OK? How the heck does the sensor work anyway?

Just wondering.

J.

 

Did you check the pressure of the spare?

 

Didja ever READ the OWNER'S MANUAL about that little light?

And no, your eyeball is NOT an air pressure gauge.

Oh, I dunno. What does your OWNER'S MANUAL for your SHINY NEW $25,000
TOY say?

 

My TPMS light will come on occasionally on my 08 EXL V6 when the temperature
drops to -35 or -40 and once it warms up to a balmy -20 the light goes out.
I was thinking of having nitration put in and see if that would make a
difference.
just a thought

Cheers

 

Er, yeah. Well, out here in Los Angeles, I suppose when the Richter
8.0 hits it's likely to cause the TPMS light to come on, too. I'll let
you know.

J.

 

Speak for yourself.

You're not going to fool me like that, I know how that worked out at
the end of Raiders of the Lost Ark!

OK, I understand there's some federal mandate that we have these
things, and I guess they work by emitting deadly radiation and
reporting my whereabouts to the FBI at every moment. Just as in five
years, we'll have the same devices rammed up our asses for Obamacare.

But I was just wondering (a) why the light didn't go out right away,
that is still lit up the next time I started and drove a few feet, and
(b) why my dealer doesn't ever open up the users manual or read the
plaque inside the driver's door giving recommended pressures.

... and I'll see if I get back that 1-2mpg now that the pressure is up
where it ought to be.

J.

 

Speak for yourself.[/QUOTE]

So your eyeball can tell the difference between 35psi and 32psi?

SURE it can. <snort>

 

hmmmmm, what does your OWNER'S MANUAL say?

Excellent question. Ask him.

 

The TPMS will sample tire rotations once the car's speed is over
30 mph for about a minute. If it likes what it sees, it will then turn the
light off.

Some tips:
* Use a hand-held gauge (NOT the one on the air pump), and use the same
gauge for all the tires.
* Check and set the pressures COLD and OUT OF THE SUN. First thing in the
morning before the sun hits the tires is best. If you must add air when the
tires are warm, set the pressures TOO HIGH, then bleed off some air the
next morning to arrive at the final pressures.
* An ordinary bicyle pump is great for fine-tuning the pressures a pound or
two at a time.
* Inspection by eye is NOT reliable; tires will only be obviously visually
low once they're down to about half their proper pressures.

Another important tip: Occasionally, one tire will "settle" to a final
rolling circumference that is different from the others. This can cause
sufficient rotational differential from the other tires that can fool ABS-
based TPMSs into thinking that tire is low. You can check this by carefully
measuring the distance from the ground to the top of the wheel rim on each
of the two tires on an axle. This must be done with the car on a perfectly
flat surface, such as the concrete pad of a gas station.

 

I F***ING KNEW IT! THANKS, BRO!

One word - prepare!

 

Could we possibly make tire pressure any more complicated? These tpms'
are bs.

 

Write your Congressman. Congress is who imposed it in the first place.

 

Thanks, Tegger.

I gathered from my experience that some speed or distance is
necessary. I wonder at the devices, do they need the rotation to
generate the power to send a signal? Yet the web page for the
manufacturer suggests they have a device that queries them at rest. I
still don't know how they get the signal to the dashboard, some form
of RF I guess, bluetooth or some other frequency.

Yes, I do.

Good idea. I knew I should have put another pound or two in, to
guestimate the right numbers "warm".

Ha. Takes a fair amount of pumping a hand-pump to move a car tire
1psi, and the connections often leak just about that fast.

Sure, but I assumed that three tires were good and one was lighting a
sensor, and you'd think that might be visible. In my case they were
all just about equally low so there was no real visible difference.

I don't grok this, why would rotational difference set off a pressure
sensor, do these things cross-check each other? I can't figure why
that would help.

So, do the dealers have a lot of customers with these kinds of issues?

When I next bring this car in for service, I'm going to mention the
low pressure to the service manager and the front office. The only
way the four wheels had the same low pressure, is if that's how they
gave it to me. I do recall in the past, some guy at the dealership
said they ran them low because "it gave a smoother ride". Guess he's
still working there. Can't be good for the tires.

J.

 

I'll add it to my airbag letter.

J.

 

But good for the bottom line (selling new tires). BTW, I suspect lots of
owners appreciate the "smoother" ride.

 

There are two kinds of TPMS. One is ABS-based (rubber valve stem), and
the other is transponder-based (steel valve stem).

Transponders are incorporated into the valve stem. They work a bit like
cell phones, in that they have batteries and emit a radio signal. That
signal is received by the TPMS computer. Eventually, transponder
batteries will go dead and need replacing. Draw on the batteries is
tiny, so it will be years before they go dead. But when they do, imagine
all those irate customers! Thank you, Congress.

ABS-based requires actual tire rotation to determine if one tire is low.
Transponder-based does not require tire rotation. As I understand it,
transponder-based systems wait a bit before deciding that there's a
problem, even though they /could/ snitch immediately if they wanted to.
I'm not sure why.

My Schwinn pump does about six pumps to the pound. I consider it
cardiovascular exercise.

There is no appreciable leakage from the valve stem when the pump is
connected to it.

Nope. No obvious visual difference until they're about 15psi low.

Rotational difference is used on ABS-based systems. ABS-based systems do
not have sensors inside of each tire. Measuring and comparing rotations
is the only way they have of being able to tell if a tire is low.

Transponder-based systems measure tire pressure directly, using sensors
inside of each tire (and sometimes even inside the spare).

Yes. Just like EVAP.

If he said that, then he's a dummy.

Probably not. But this monkey is not too smart if he thinks he's smarter
than the Honda engineers that designed your car. I'd trust the Honda
guys before I trusted some goofball working for a dealership.

 

Must disagree. I can't tell pressure on some arbitrary tire on an
arbitrary car, but I can get used to what my own tires look like
properly inflated, and notice a different curve as they get low. I've
had to deal with leaky tires before and had practice.

OK, I see. Sort of. Funky.

I think the logic is that Honda has to overinflate them to get the EPA
mileage up, but that for a mile a gallon or two, you can get a better
ride with lower inflation.

Might even be somewhat true, but even so, they overdid it.

J.

 

So your eyeball can tell the difference between 35psi and 32psi?

SURE it can. <snort>[/QUOTE]

Mine can. There's this little LCD that I look at.

Erh, wait, that's what you were talking about using.

I can tell the difference beween 32 psi and 24 psi.
--

- dillon I am not invalid

The RMS Titanic sank on April 15th.
Taxes are due on April 15th.
Coincidence? I think not.

 

There's going to be a run on KY. And Astroglide. And probably 30 wt.
--

- dillon I am not invalid

The RMS Titanic sank on April 15th.
Taxes are due on April 15th.
Coincidence? I think not.

 

Thus spake :

I know you're talking C and not F. Oh, that's still fracking cold.

Mine will usually come on around 20F if the pressure is near the
trigger point. Sometimes I can warm the tires a little (if you've
seen any kind of auto race, you know how).

BTW, my light came on yesterday. Since it hit about 70F, I don't
think it's the temperature. But I'm waiting until this morning when
they're cold to air up.

--

- dillon I am not invalid

The RMS Titanic sank on April 15th.
Taxes are due on April 15th.
Coincidence? I think not.