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I recently had the Tire Pressure Monitoring System (TPMS) fail while I was on Highway 400, resulting in a blowout and the destruction of the tire. They are designed as a safety feature to insure that car owners will maintain correct tire pressure, but since they can unpredictably fail, they are a safety hazard. If you are involved in an accident and if you have ignored the low pressure warning light, your insurance company can discover this from your car's computer and refuse to cover a claim. – Gary, London, Ont.

That yellow Tire Pressure Monitoring System light isn't a friendly warning to put a little air in the tires – it's an emergency warning that a tire has lost at least a quarter of its pressure, says the Rubber Manufacturers Association.

"It's a warning light for a reason," says Dan Zielinski, spokesman for the association, which represents tire makers in the U.S. "If you've been checking your tire pressure monthly and that light comes on, in all likelihood, the tire has picked up some kind of damage and is leaking.

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By U.S. law (the aptly-named TREAD Act, short for Transportation, Recall Enhancement, Accountability and Documentation), the TPMS warns when a tire is under-inflated by 25 per cent. That's a lot lower than your tires should ever be – and that's why TMPS shouldn't replace the tire gauge in the glove compartment, Zielinski says.

"Some drivers use that TMPS light as a substitute for a tire gauge and letting it run down until the light comes on and then filling it back up," Zielinski says. "But by the time that light comes on, you could have been driving on seriously under-inflated tires for months."

Air holds tires together. Driving for long with low tire pressure – even 10, 15, or 20 per cent – can weaken tires. A tire can blow out because of accumulated damage – even though the pressure at the time of the blowout isn't low enough to trigger that TMPS warning light.

"The damage has already been done," Zielinski says.

The best way to prevent tire damage? Check tire pressure monthly. For the most accurate reading, do it before you drive anywhere (not after you've grabbed a latte), because the tire pressure increases as the tire warms up on the road. Fill up to the cold pressure recommended on the sticker on the driver's door. Don't use the number on the side of the tire – it's the maximum for that tire. If you're regularly losing tire pressure, it could be a sign of a slow leak. Get it checked.

When that light comes on while you're driving, and stays on, take it seriously, Zielinski says. Pull over and check the tire pressure with a gauge.

In a direct system, the light is supposed to come on if the car loses the signal from a TPMS sensor, because of interference, failure or a low battery in the sensor.

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Transport Canada is investigating complaints of TPMS failures because of corrosion. None of those failures resulted in an accident, it says.

If you do get into an accident and you've ignored that TPMS light for months, it's not likely to affect your claim, says the Insurance Bureau of Canada (IBC).

"You should check your policy, but I've never heard of a claim being denied for this here," says Pete Karageorgos, manager, industry and consumer relations with IBC. "It would be the same as other mechanical stuff, like being overdue for an oil change or needing a brake job."

Send your automotive maintenance and repair questions to globedrive@globeandmail.com

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