Tire Light 2007 SR5

POS Racing

POS Racing

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My sister's '07 2wd SR5 V6 has kicked on the low tire pressure light, she had a local tire shop check all the tires and they claim they are all at 32 psi. including the spare...... :confused:

I told her to try another tire place to see if they may find something the first on missed, but with only 5 tires on the truck this doesn't seem like a tough problem to solve if the system is working correctly. :bash:

Any thoughts on why the light would be on if all the tires are at recommended pressure?

TIA!
 
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At first I thought: How would the computer know if the spare is flat...

Then I thought, wait... how does the computer know when any tire is flat?

Well?
 
There is a tire pressure sensor around each valve stem and they report when the tire pressure gets below 27 or 28 psi. When any one tire (including the spare) gets below that set PSI, then the light on the dash goes on. It would be nice if it told you which tire, but unfortunately it does not.

Uh, why can't she check the pressure herself. I understand she's a girl, but that ain't a good excuse in my book.
 
Since 2004, the 4Runner has had valve stems with radio transmitters in them that send a pressure reading back to an ECU. If any one of the 5 transmitters reports a value less than 27 PSI, the light comes on. In theory, if any one of the 5 transmitters is missing (dead battery, stolen spare, etc. - yes, they have unique ID numbers) or reporting garbage, the light flashes.

A search for "TPMS" (Tire Pressure Monitoring System) will bring up many threads.
 
Ah yes. One of my current prof's worked on the project that implants small RFID based devices into tires, an extension of the animal tagging system. Cool stuff.
 
sharp4runr said:
Uh, why can't she check the pressure herself. I understand she's a girl, but that ain't a good excuse in my book.
Click to expand...
She did but she can't get to the spare... So she took it somewhere to have them do it and they told her it was fine...
toto said:
Since 2004, the 4Runner has had valve stems with radio transmitters in them that send a pressure reading back to an ECU. If any one of the 5 transmitters reports a value less than 27 PSI, the light comes on. In theory, if any one of the 5 transmitters is missing (dead battery, stolen spare, etc. - yes, they have unique ID numbers) or reporting garbage, the light flashes.

A search for "TPMS" (Tire Pressure Monitoring System) will bring up many threads.
Click to expand...
Yea I did search it, and the light isn't flashing.

I'm betting they are not checking the spare. As most shops tend to do they just tell the nice lady they checked it took her $$$ and send her on her way.... :mad:
 
You have to drop the spare to check the pressure. I kinda doubt they dropped the spare to check it. This is something you or she can do as it is also necessary to find all of the equipment to lower the spare in case you need it.
 
Didnt have to drop my spare to check it. Just went through the low tire warning light two days ago, and found my spare was low. You just have to reach in through the spokes to check the pressure, and if it's low, you have to have a "real" air chuck, the type that is about 8" long, and has an angle head with two fittings that you can either push on from the front, or pull on from the back. Available at any auto parts store. I filled up my spare to 35psi right where it sat with no problems or oddities at all with that air chuck.
 
Yeah last year this the TPM light came on and it was the spare. I pumped it up to 40psi and never had a problem the rest of the winter. I figure it's better to be over pressurized than under.
 
sharp4runr said:
Yeah last year this the TPM light came on and it was the spare. I pumped it up to 40psi and never had a problem the rest of the winter. I figure it's better to be over pressurized than under.
Click to expand...

40PSI is fine.
 
cmar said:
The light will come on if there is a difference of 4 psi between the 5 tires also.
Click to expand...

Please explain? So you mean, let's say if all my tires are 35, but my spare's like 30 or 29, technically the light shouldn't come on, because someone mentioned that it comes on below, 27 or 28, but you're saying that it will even come on if one of the tires has a 4 psi difference between all 5 tires??:confused: :confused: :confused:
 
The service manual doesn't mention anything about a large differential turning on the light.

The less-desirable, "passive" or "indirect" TPMS systems detect a low tire by measuing the rotation speed of each wheel as recorded by the ABS computer. A big enough difference in pressure would manifest itself by a different speed, so the system would know if a tire was low. Of course, this method fails if all 4 tires are low, and it can also give false readings based on driving conditions.

Some of the first Toyota/Lexus products with TPMS used this indirect method. The 4Runner has always had "direct" or "active" TPMS, which uses radio sensors to measure and record the actual air pressure in each tire. I believe all Toyota/Lexus products now use the active method.
 
My previous 2005 had the light on and all pressure was fine. It turned out to be a small piece of nail with the head broke off. It wasn't leaking but I was told that the sensor could determine it was there. Not sure how accurate that is but when we found it, the problem was resolved.
 
You can check the pressure in the spare without droping it. I did it last week. Get a tire gauge for a large truck with the double ended head. You can get to the valve stem on your back. I pump my spare up to the max on the sidewall of the tire (the dunflop tire reads 51 PSI max). Then you will for sure have enough pressure a year or more latter. Just keep a tire guage in the glove box. I would much rather let some pressure out than have a flat spare, or get one of those small $10-15 walmart 12v air compressors. They fit perfectly in the passenger side rear storage compartment and it is better than nothing in a side of the road situation.
 
What i mean is if all your tires are 35psi and one is 4psi lower or higher than all the others then the light will come on. Even if they were all 20psi, same concept.
 
cmar said:
What i mean is if all your tires are 35psi and one is 4psi lower or higher than all the others then the light will come on. Even if they were all 20psi, same concept.
Click to expand...

I don't think it works that way. I have pumped the rear tires to 40PSI and left the fronts at 32 when towing and never had a tire pressure warning come on.

I will go one step beyond that in the morning. I will pump the back up to 45psi and set the fronts to 29 just to see if it lights, Then drop 1/2 a pound at a time to see when it lights.

I have the day off anyway. Got to have something to do.:D
 
Let me know if that works.. i may have the wrong info, but its just what i was told a the Heyward Allen dealership in athens ga.
 
It doesn't understand the differential of pressures. Like I said in my other post, I filled up my spare to 40 PSI and the light went off. The other 4 tires were at around the suggested pressure of 32psi. light should only come on if any one of the 5 are below 27 or 28 psi.
 
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