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Full Compliance with US Tire Pressure Monitoring Systems Regulation Coming Into Effect

With the TPMS, one of these symbols will light up on the dashboard when any tire is 25% under-inflated.

September 1 marks the start of required 100% compliance with the US federal mandate for all new vehicles of 10,000 pounds (4,536 kg) or less gross vehicle weight to have a four-tire pressure monitoring system (TPMS) that is capable of detecting 25% under-inflation and warning the driver.

The TPMS rule (FMVSS 138), crafted in 2002, began its phase-in in 2005. The rule is designed to address fuel economy and safety issues caused by under-inflated tires. Fuel efficiency is reduced by 1% for every 3 psi under inflation, according to the industry.

In terms of safety, dry and wet handling performance also suffers with under inflated tires. The types of crashes that under-inflated tires influence include skidding and/or loss of control, hydroplaning on a wet surface, and crashes from flat tires or blowouts.

The rule is technology-neutral, allowing any TPMS design that complies with the performance requirements. Performance testing is to be done with tires on vehicle at time of first retail sale.

There are two basic types of TPMS: Wheel-Speed Based (WSB, referred to as “indirect”) and Pressure-Sensor Based (PSB, referred to as “direct”).

Wheel-Speed Based TPMS infer tire pressures using the vehicle’s ABS hardware, specifically the wheel speed sensors, to measure tire-to-tire differences in rotational velocities. Pressure-Sensor Based TPMS directly measure tire pressures with pressure sensors mounted either in each tire or on each wheel.




"Fuel efficiency is reduced by 1% for every 3 psi under inflation, according to the industry."

The numbers are transposed - should be the other way around...


wow, never realized that this would be a requirement. nice!


Just another idjit light among dozens that will be ignored by many people.

My wife's RX330 has this feature. One day she calls me up and asks, "What's this horseshoe that's been lit up all week on the dashboard, anyway?"

Not knowing what a 'horseshoe' light was, it took some digging in the manual before I realized what she was referring to. Turns out that when NTB put new tires on the car, they didn't know that the tire pressure monitoring system needed to be reset.

Bob Bastard

In addition to wasting fuel and posing a safety issue, under-inflated tires also wear prematurely. Nice to see this as standard equipment.


The sensor should be wired into the engine software so as to limit the top speed.

Stan Peterson

This is an example of "job justification" and "mission creep". All US autos will need to have Stability Control as standard equipment by 2012. Stability control includes anti-tipping, ABS brakes, and anti-skid technology. That technology is at least comprehensible as a "safety system".

This tire pressure regulation much less so. But both serve to provide work for bureaucrats, enforcing the new regulations, now that their primary needs have been accomplished.


Your cynical view doesn't seem to meet those of most users of this site who are interested in fuel-economy and safety. Would you regard ABS and airbags as bureaucratic hindrances too? There's a long list of benefits to both safety and fuel-economy in the article (if you read it) with little cost needed for the version that uses the ABS hardware. In fact the only costs are the dashboard lights and a software change.

Governments CAN do good things too you know!


What justifies the job of the person who spends time reading and commenting on blogs?


Perhaps some folks comment in an attempt to be helpful. I do not know exactly how under inflated tires contributed to the SUV roll over issue a little while back, but I think letting a person know a tire is under inflated, especially a front tire, might actually reduce some "lost control" type of accidents.

Yes, the use of symbols rather than English words is unwise. I have a little light come one, it looked like a car, and I drove with it until my next scheduled maintence. What it turned out to be was a warning light, my brake lights were burnt out. So I was needlessly putting others at risk, and risking a citation as well, because I cannot remember the meaning of symbols. Language is an amazing invention. Letters grouped into words. This is a great way to convey information. How about a warning signal that says "Low Tire Pressure" or "Brake Light Out"!!


you are absolutely right !
how much would it cost to put a mass produced LCD on the dashboard displaying the ECU error codes, in English or whatever language ? $5 bucks ?


Van. The SVU rollover issue , specifically Ford Explorer with Firestone tires story. During pre production testing , ford found that the explorer had un-acceptable handling and ride with fully inflated light truck tires. (I bet they tested more than firestone, but firestone was the ford tire vendor at the time).

The engineers at Ford found that at 26 psi , just like magic, handeling improved, just enough understeer to slide instead of roll.

The problem is, 26 psig on a tire designed for 32-36 psi will run hot. And 26 psi can turn into 15-18 over time because most people don't check pressure often.

At far less than 26 psi, tire failure due to overheating , often at high speed , an just like magic, lot's of rollovers with severe injury and death.

The Ford was paying off in lawsuits , always with a clause to keep settelement secret. Then one family refused , and it hit the fan big time.

Ford and Firestone/Bridgestone knew this for a long time , and did nothing until forced to. They Blamed the tires, but it was stupid risky Decisions at ford.

The newer Explorer with indipendent rear suspension does not have the same problem.

Corporate culture runs deep , and often never changes.

Bill W

This is not intended to be a negative comment, but could you not spend 5 minuets to read your car's manual to discover why the warning light was on?

Actions like that are the reason we have to live with useless government "safety" requirements such as this articles tire pressure warning system. As stated above, most people will ignore the light anyway.

Because people did not spend 30 seconds to glance at their tires, the tires failed and people where killed and injured.

The facts show that the tires were marginal and Ford was pushing the limits by reducing pressure in an effort to makes it marginal product palatable, but if the recommended tire pressure was maintained, would anyone have been hurt?

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