Low Tire Pressure Warning System

[Rest]

How does this system work? Do we get an idicator light based when a tire or tires pressure reaches a set minimum? Or does it warn us based on a difference in pressures between all four tires?

[Charles Suitt]

See Pages 150-152 of your 2007 Owner's Manual. Sensors are located inside your wheels at the base of the valve stem.

[Rest]

I know where the sensors are located.

I should point out I had a leak in one of my rear tires. It turned out to be a nail and I had it repaired. The warning light came on again a few days later and the tire pressure was not low. The repair place said that maybe the system detects one tire that is not near the same pressure as the others. So they lowered all the other tires pressure to factory specs. I don't think that is how the system works. I believe each tire is independent of the other and you get a warning when the tire pressure goes to 25% of what was put in. But I think the place that fixed it put lower than what I had in to start with (42 front/ 40 rear). So I am thinking that is what set off the warning. I am guessing but I believe I have to reset the warning system.....yes?

One note, when I raised the tire pressures to 42/40, I never reset the system and didn't get any warnings.

[JimN]

<div class='quotetop'>QUOTE(Rest @ Mar 6 2007, 05:40 PM) [snapback]401227[/snapback]</div>

I know where the sensors are located.

I should point out I had a leak in one of my rear tires. It turned out to be a nail and I had it repaired. The warning light came on again a few days later and the tire pressure was not low. The repair place said that maybe the system detects one tire that is not near the same pressure as the others. So they lowered all the other tires pressure to factory specs. I don't think that is how the system works. I believe each tire is independent of the other and you get a warning when the tire pressure goes to 25% of what was put in. But I think the place that fixed it put lower than what I had in to start with (42 front/ 40 rear). So I am thinking that is what set off the warning. I am guessing but I believe I have to reset the warning system.....yes?

One note, when I raised the tire pressures to 42/40, I never reset the system and didn't get any warnings.
[/b]

The warning lights when pressure drops 25% of the set value in any one tire. At 42/40 you will have to lose more than 25% before the light comes on. Ensure all the tires are at the desired pressure then reset the sensors as per the owners manual.

[Rest]

Okay so after I raised the pressure to 42/40 if I wanted to keep that 25% loss warning then I had to reset the system. It all makes sense now, thanks.

One more question. When one of the sensor batteries goes dead how can I tell which tire the sensor belongs to, without taking my Prius to a dealership?

[Bill Merchant]

<div class='quotetop'>QUOTE(Rest @ Mar 6 2007, 02:40 PM) [snapback]401227[/snapback]</div>

I never reset the system and didn't get any warnings.[/b]

You have identified why you got the second warning. EVERY TIME you change the pressure, rotate the tires, get a flat, boost the pressure, drop the pressure, get new tires, etc., etc., take 15 seconds to reset the system. The TPMS doesn't know what your tire air pressure is, only if it decreases from when it was reset. No reset, it can get confused.

Regarding battery life, ask this question again in a few years. Those are long-life batteries. You'll run the tread off your Integrity tires long before the battery wears down.

[Allannde]

<div class='quotetop'>QUOTE(Rest @ Mar 6 2007, 09:27 PM) [snapback]401457[/snapback]</div>

Okay so after I raised the pressure to 42/40 if I wanted to keep that 25% loss warning then I had to reset the system. It all makes sense now, thanks.

One more question. When one of the sensor batteries goes dead how can I tell which tire the sensor belongs to, without taking my Prius to a dealership?
[/b]

Actually, you can't. If a sensor battery fails, the warning light will be on all of the time. Check your tires. If they are all okay, the only way to know which wheel has a failed sensor battery is to take the car to a dealer who has a scan tool who can get a reading from individual wheels. Even then he will need to maipulate the pressures to figure out which wheel is which.

Except if you encounter a faulty battery in a sensor, this is a long way off. I think they are supposed to last ten years.

[Rest]

<div class='quotetop'>QUOTE(Bill Merchant @ Mar 7 2007, 01:33 AM) [snapback]401463[/snapback]</div>

Regarding battery life, ask this question again in a few years. Those are long-life batteries. You'll run the tread off your Integrity tires long before the battery wears down.
[/b]

Rarely will anyone get the rated 10year life out of the batteries. Other vehicles use similiar systems with the same type 10 year battery and only get 3 to 5 years life.

[Bill Merchant]

So, when you replace your tires, you can prophylactically replace the battery. What's the problem?

[Bear68]

<div class='quotetop'>QUOTE(Bill Merchant @ Mar 7 2007, 03:26 AM) [snapback]401525[/snapback]</div>

So, when you replace your tires, you can prophylactically replace the battery. What's the problem?
[/b]

Problem is............. you cannot replace just the battery in a tire pressure sensor. You have to replace the sensor.... About $150 each if memory serves me correctly.