Manny-n-Mel

OK, folks, I'm new to the forums and this is my first post. Because of recent experiences with both automoticve forums and dealers, I know the best place for answers is from those that actually own the cars and drives them as often as I do, so this is why I come to you. I will warn you, I get a bit long winded:

I am the proud owner of a brand new '07 Flint Mica tC. My recent car was a '00 VW Beetle. I loved that car, and I drove it like I loved it. By the time I got the tC, the beetle had well over 165k miles on. So, I think it's fair so say that I love to drive my cars. Due to its increasing unrealiability and my inability to take the time off to take it to the garage to make any repairs I invested in a Scion, and I am just as happy as ever. But the first thing I wanted to do was change the wheels over to the tC. I contacted the wheel manufacturer, RONAL, and ordered a set of lug nuts and hubcentric ring inserts so I could make the switch on an available weekend.
Once switched, I realized that this was my first mod (insert trupets blairing). I drove around for a few miles to make sure that there was no wobble in the streering wheel and scheduled an appointment to have an alignment done this weekend. Everything was going great untill yesterday morning.
I have a long drive to work (about 1 1/5 hours if I'm lucky.) About 45 minutes into the drive, the tire pressure warning light started flashing and eventually stayed on. I checked the manual, it says that there are sensors in the valve stems of each tire that transmit a signal to the ECU to monitor the tire pressire. Yet almost every post I have read on these forums describe the sensors being located on the brake system (or other location on the car itself) in order to monitor wheel spin ratios, which to me seems more logical. My first question is - Which is it? Exactly where are the sensors and what exactly do they monitor? (OK, I guess that's three questions.)
Next, I followed about three different procedures on reseting/recalibrating the sensors as described on these forums and the manual. All describe the warning light flashing three times. The problem is when the key is turned to the ON position the light starts flashing (about twice per second) but when I press the reset button in the glove box, it slows to about one flash per second. After about three flashes, the speed increase to what is was before and eventually the light stays on.
Tire pressure in all four tires was checked and adjusted as needed and I made sure that there was no more than a +/- of .5 # differnce in any of the tires. I know the car will need the alignment, but that won't happen until the weekend.
Next question: What else can I do? With all I've described, is there anything anyone else can suggest? I realize I may just have to take it to the dealer, but that's something I'd like to avoid if at all possible.

engifineer

I heard that on the 07 they actually used tire pressure monitors rather than just monitoring wheel speed. On the 06 and earlier, they use the same method most cars do. They use the wheel speed obtained for each wheel by the ABS system. If one wheel begins spinning faster than the rest over a given amount of time, then the pressure is deemed low and turns on the light. If yours has a true pressure monitoring system it is different. Dont quote me on it, but I am thinking that is one of the changes on the new tC.

Manny-n-Mel

D@mn! I guess that means a trip to the dealer after all. Thanks for the tip.

If anyone else out there knows a way to get around the TPS light, that DOESN"T involve covering up or cutting anything, please let me know.

-OR_

If anyone else with an '07 tC had this happen to them, please let me know.

Thanks...

surfcity40

welcome. here's a link that explains how the 05 and 06 system operates. the speed sensors are at the hubs in the 05 06. i had not heard there was a change in the 07 system.
https://www.scionlife.com/forums/viewtopic.php?t=120624

"quoting from the manual CHASSIS- tire pressure warning system, pages CH-52 to CH-57:" when the tire pressure warning system detects a drop in the tire inflation pressure while the vehicle is in motion, a tire pressure monitor ECU turns on the low tire pressure warning light. the tire pressure monitor ECU, which is enclosed in the skid control ECU, controls this system. the skid control ECU is integrated with the brake actuator. the tire pressure monitor ECU calculates the tire inflation pressure based upon signals from each speed sensor.
how it works basically, is by using a "relative wheel speed difference(rolling radius difference method)"....when the tire inflation pressure drops, the actual radius of the tire decreases. as a result, the wheel speed increases. the tire pressure monitor ECU compares the speed of each of the four wheels, and detects a drop in the inflation pressure from their difference.
most of the components of this system belong to the brake control system. therefore, this system does not have a designated diagnosis function."
the parts fishe on the site (click "features" then "tech" at the top of the page ^) does not show a change yet.

here is the correct procedure for reinitializing the tire pressure warning system.
http://home.cfl.rr.com/icdedppl/faq.html#c15
(you'll want to bookmark that FAQ).

Manny-n-Mel

NEW INFO...

I completely forgot that a friend of mine actually works for Toyota. I gave him a call and asked him to hit up one of his tech friends for some info. He was told that many of the new cars and trucks actually do have air pressure sensors in the valve stems of each wheel that sends a signal to the ECU (as descibed in the manual for the '07 tC). He said that he would confirm if there was a way to disable the sensors or at least the warning light and get back to me. He did say that the dealer could install the sensors on my wheels, but that he couldn't say what the charge would be, but that he would find out that info as well. So for now, until I get a straight answer, I guess I'm stuck driving with the TPS warning light on.
If anyone else has more info, please pass it on. Thanks.

Tomas

There *IS* a TBS on the new pressure sensing system on the '07 tCs...

PD038-06 TIRE PRESSURE SENSING TRANSMITTER ACTIVATION PROCEDURE
6/1/2006 - 2007 model year Scion tC vehicles.

A tire pressure sensing transmitter is built into each tire valve, and the measured tire pressure data is transmitted through a Tire Pressure Warning System antenna to the Tire Pressure Warning System receiver.

The tire pressure sensing transmitters used for the Tire Pressure Warning System
(TPWS) on 2007 model year Scion tC vehicles need to be activated during
Pre-Delivery Service (PDS).

The '07s ARE different.

Tomas

surfcity40

thanks for the updated info Tomas. with the sensor using a transmitter now i don't see how changing out the hub would be the issue. i could see it being the issue on an 05/06 because of the location of the sensor. maybe it wasn't initialized at delivery.

Tomas

Yeah, with the change of wheels on the tC, his pressure sensors are still on the old wheels - whever they are, hope he still has 'em.

New owners of '07s need to be warned that the supplied wheels have the sensors attached to them, and the pressure monitoring system will go into 'panic mode' when it can't find the signal from them.

Tom

surfcity40

with the number of scion tC drivers that change out their wheels, it may need to be stickied somewhere that 07 drivers need to use the valve stems provided with the car because there are expensive little transmitters in them. i see this becoming a very common problem/thread.

Tomas

Ayup!

Could be bad.

I'll come up with some sort of warning post to stick, but then I need to decide if it should be stuck in 'tires' or 'tC.' *sigh*

Tom

Tomas

===> https://www.scionlife.com/forums/vie...767032#1767032

Manny-n-Mel

Damn! Of all the years i decide to get a new car, i get the one what will be the most sensitive to mods!

You're right, when I started this thread, I only expected a couple of replies. When I checked this morning and saw the the number had doubled, you could have knocked me over with a brick.

Yes, I still have the old tires. They were set to go up on ebay this weekend.

I guess I'll have to shedule a trip to the dealer after all.

Thanks everyone for the input. I'll let you know how things work out after I make the switch.

engifineer

If they are in the valve stems.. that pretty much sucks... are they removable? Or part of the valve assembly? I have my stems replaced every time I replace my tires, that is pretty much common practice in a good tire shop.

Tomas

Manny, if you could somehow manage to take a pic of whatever these 'things' looks like, that might be a great help to everyone else who buys a 2007 tC.

THANKS!

Tomas

Manny-n-Mel

Way ahead of you on that one Tomas. I already have plans to take them to a tire shop after work and have the "inspected" for these mysterious sensors.
I also have a call into my friend that works for Toyota to see if they'll make the nessessary switch or if they can even be switched to the new wheels at all.

Honestly, I don't see why they wouldn't be able to change them. When they released the tC it's obvious they had tuners in mind. I doubt they would have made it impossible to change a part that would most likely be one of the first, if not the most important (in my opinion) mod to any car.

As always, I'll keep you informed.

Tomas

Some examples... (not Toyota/Scion)...



Most have lithium batteries inside each transmitter, and battery life of 5 years is expected...

Here is a tech writup at TireRack covering both the old and new system types used in the tCs:

http://www.tirerack.com/tires/tirete....jsp?techid=44

Near the bottom of the article you will see a pic of the units used in Lexus cars. I suspect those in the tC are the same, or at least similar.



Note that the tire valve mounted units will NOT fit all wheels and that they can change the weight required to balance a wheel/tire assembly quite a lot...

Things are getting more interesting when changing wheels...

Tomas

P.S. Improperly or carelessly used tire changing equipment can easily destroy these units, so one should always be sure to warn the tire folks that your wheels have these units...

T

surfcity40

given the scion philosophy of individualization this change is a surprising one. the old hub mounted sensors were not affected by a wheel change. they merely had to be recalibrated sometimes. it's odd to me that scion would use the lexus system when it's common knowledge that a majority of tCs get a wheel change.

Tomas

The new federal requirements may be having some effect on that change, but I don't know that for sure.

It does give one more thing that 'modders' and accessory manufacturers have to pay attention to. It's not just 'bolt pattern, diameter, width, offset' anymore, but 'sensor fit' has to be a part of the mix that is looked at.

Guess I need to find the FMVSS section that very soon makes the sensors mandatory, to see what sort of requirements there are. *sigh*

(It is odd that this change to individual pressure sensors is being made, since ANY car with ABS - which is the vast majority of new cars - can detect wheel-speed variances with only minor effort. The only thing that might make sense is some sort of requirement in the new federal standards that the ABS based systems can't meet.)

Tomas

surfcity40

possibly, but any system is still unavailable on most vehicles. it may be as simple as toyota choosing to use one system for all of their brands, as opposed to two, and choosing the wheel sensor over the hub sensor. it may just be a more accurate way of monitoring tire pressure.
btw, thanks for the photos Tom.

Tomas

The FMVSS requires that as of 01September 2006 70% or more of the manufacturer's production must have the TPMS (Tire Pressure Monitoring System) meeting requirements of section 138.

Those requirements require actual monitoring of tire pressure, and cannot depend on the hub-mounted rotational speed method.

For those who enjoy reading the federal standard, here's a copy (.PDF).

Looks like the change of monitoring system is demanded by federal standard, folks. Enjoy it!

Tom