Tire Pressure Sensors

[tiger862]

On the 2012 Impala I have to set to dash readout. It is a pain as door jam says 30 psi and that is what you set it to. One gauge showed 30 she drove it to work read RR low so checked and was right so I looked at gauge and it showed 25 psi cold so I went to 40 on gauge then showed 30 psi. I replaced gauge then next oil change set to 30psi to gauge she told light came on to high pressure (showed 32psi cold) so I had her watch readout and when it hit 30psi I went to next tire now no more light. What I learned was her has instant pressure readings and you need a tool to put tire in corrected readout. I don't have tool but still know when a tire is low just have to check all 4. Love the Caravan one with light,check 4 tires then drive, problem solved.

 

[Shannow]

I seriously doubt that the majority of TPMS, or very many at all use the rolling radius to infer tyre pressure.

Mine (Colorado), I can air down and air up without turning a wheel and have the pressure change as I go....it's NOT measuring rolling radius.

 

[billt460]

Originally Posted by Shannow
I seriously doubt that the majority of TPMS, or very many at all use the rolling radius to infer tyre pressure.

"Indirect TPMS works with your car's Antilock Braking System's (ABS) wheel speed sensors. If a tire's pressure is low, it will roll at a different wheel speed than the other tires. This information is detected by your car's computer system, which triggers the dashboard indicator light."

This say's otherwise. I'm not saying you are wrong, but how else could one tire roll at a different speed than the others if they're all the same size?

 

[Snagglefoot]

Originally Posted by billt460
Here is another question. A few months ago I rotated my tires. Front to back criss cross. Did that screw anything up? Are they still reading as shown on the dash, or do I have to develop a "secret code" now?.... (LF = RR..... RF = LR).


On my Suburban. there is a sequence to reprogram the sensor in the new position. You set it up on the display, drop the tire pressure a bit, and the horn honks to indicate the new position. Repeat with all four corners, then air up. Check the internet for your vehicle. It might have a procedure.

 

[billt460]

Originally Posted by Snagglefoot
Originally Posted by billt460
Here is another question. A few months ago I rotated my tires. Front to back criss cross. Did that screw anything up? Are they still reading as shown on the dash, or do I have to develop a "secret code" now?.... (LF = RR..... RF = LR).


On my Suburban. there is a sequence to reprogram the sensor in the new position. You set it up on the display, drop the tire pressure a bit, and the horn honks to indicate the new position. Repeat with all four corners, then air up. Check the internet for your vehicle. It might have a procedure.

Thanks. When I adjusted, (increased) my tire pressure the other day on my Jeep, it showed my left front to be about 3 PSI higher than the others. So I bled some out. I'm going to drive it today, so I'll see if it registered correctly on the dash. If not I'll look into it.

 

[Shannow]

Originally Posted by billt460
Originally Posted by Shannow
I seriously doubt that the majority of TPMS, or very many at all use the rolling radius to infer tyre pressure.

"Indirect TPMS works with your car's Antilock Braking System's (ABS) wheel speed sensors. If a tire's pressure is low, it will roll at a different wheel speed than the other tires. This information is detected by your car's computer system, which triggers the dashboard indicator light."

This say's otherwise. I'm not saying you are wrong, but how else could one tire roll at a different speed than the others if they're all the same size?


Sorry mate, never seen or heard of such a system...only ever seen the direct method.

Given that the tyres rolling speed changes as you corner, it's can't be anything resembling the 1psi that we see.

Looks like the Indirect was dying out but is making a resurgence
https://www.tirereview.com/indirect-tpms-imports/

Law requires it notify you when the tyre is 25% low...that's all the manufacturs will supply.

I agree with the direct being really handy...I had a nail in a couple week old tyre...the TPMS alerted me to it, but also gave me confidence in getting to a repair place.

 

[billt460]

I ran my Jeep today and the tire pressure was identical on all 4. So the system is self correcting when you rotate. I bled air out of the left front, and that is what it showed on the dash display.

 

[Fred_Garvin]

The new Volvo's work off from the wheel speed sensors. I am not sure what year they started but the 2018 V60 I drive has it. There is a calibration process to calculate offsets in RPM's due to varying tire sizes. The system will not respond to quick changes in wheel speed such as cornering but works on averaging over a period of time.

I expect this to become more common as there is less cost involved/fewer components.

 

[billt460]

This is what I've been able to ascertain on Chrysler Jeep's TPMS system. The sensors have a unique ID or serial number, that the system registers the sensors by. That unique ID is at each position. So if the system recognizes new ID's, or positions of existing ID's have changed, (tire rotation), it goes into a mode to re-register the ID's. It's a process of elimination, and one of the things it's doing is making sure its not accidentally registering ID from sensors in the vehicle that is parked next to your vehicle, or one that is just driving by at that moment. It can re-register the sensors at new positions, or brand new sensors in as little as 10 feet of driving, or as much 10 miles. In some rare cases, even more.

The sensors themselves are activated by motion. So while you're parked the sensors do go into a, "sleep mode". When you start driving they, "wake up" and start reporting. And they only report every 15 seconds or so. When your tires heat up while driving, you'll notice the pressure change reported. It will ripple through the display one after the other, with a good 10 seconds or more in between. They all just don't change at the same time. The TPMS is always monitoring the tire pressure while your driving, not just when you pull up the display. If the tire pressure drops to an unsafe, under inflated level, it may take a few seconds, but you'll get the warning lamp for tire pressure on the dash, despite not having the display up at the moment.

If you drive with the tire pressure display up and running on the dash, it does not wear out the batteries any faster, because the system is always reporting once the vehicle is put into motion. It's all pretty remarkable technology when you think about it. Especially when you factor in how little it costs in relation to the amount of information it is giving you.

Now I have to research the TPMS system in my Toyota. I'm guessing it's very similar to the system Chrysler Jeep uses, because it operates identically, and gives the same information in the same manner.