Tire Pressure Monitor Systems Explained

By Jim Taddei - January 10th 2012

Due to safety and fuel mileage concerns, in the early 2000s, the Federal government began to look into mandating on-board vehicle systems that would monitor tire pressure and alert the driver when one or more tires dropped 25 percent below the recommended inflation pressure. By 2008, this mandate went into full effect for all cars and light trucks.

The reason this became a concern at all was because of an incident in the late 1990s concerning Firestone tires. At that time, over five million light truck tires were recalled after a series of rollover accidents involving SUVs occurred. The major contributing factor to these tire failures was heat buildup, which happens when the tires lose pressure. Low tire pressure can also result in a 10 percent reduction in fuel mileage.

So why all of a sudden did we have all these issues with low tire pressure? I believe there are two contributing factors to this. First, the movement away from full service gas stations. In the past, when the attendant filled the gas tank, a quick inspection of the vehicle was done, often including a check of the tire pressure. Another contributing factor is extended oil change intervals, which increased the time between oil changes and basic vehicle inspections

The result of all of this was more and more vehicles being driven with under inflated tires. Combine that risk with tires that were more sensitive to heat buildup. Add the additional factor that these tires were commonly mounted on SUVs, which are more likely to suffer a “rollover” type crash in the first place, and you have a recipe for disaster.

So now that all late model vehicles are equipped with a tire pressure monitor system (TPMS)—what should you do when the warning light goes off? The answer is simple—stop and check your tire pressure as soon as it is safe!

When you inspect the tires after the warning light goes off, you will find one of two things:

  1. You have one or more tires with the incorrect tire pressure
  2. The tire pressures are all fine and the system has given a false alert

If the tire pressure is incorrect:

  1. If the vehicle is equipped with standard wheels and tires, the pressure should be reset to the pressure recommended on the tire pressure label. The label is located on one of the door jambs, usually on the driver’s side.
  2. If the vehicle is equipped with wheels and tires not of the standard size as indicated on the tire pressure label, they should be inflated to the pressure recommended on the tire side wall. If the tire was low and it becomes low again after you have filled it up, the tire should be checked for a leak and repaired/replaced as necessary.
  3. If a tire is overinflated (some of the newer systems will check for over inflation, also), it should be reset to the recommended tire pressure.
  4. Some tire pressure monitor systems will automatically reset the light after the vehicle is driven for a short time with the correct tire pressure. Others will require a manual reset—please consult your owners manual for the proper reset procedure.

If the tire pressure is correct:

If the tire pressures are all okay and the low tire warning light has illuminated, that would indicate a fault with the system, requiring a trip to the repair shop.

If for some reason you must drive your vehicle with the low tire light on, I would recommend frequent manual inspections of the tire pressures to be sure they are okay.

When was the last time you had your tire pressure checked?

3 User Comments

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Always nice to read your blog. Different view and an own opinion about car maintenance. Thanks for suggestions.
First , I would like to agree with the comments regarding the safety aspects of having TPMS on cars.Second ,working at a dealership and being paid on a flat rate basis , I can't stand having to waste time on checking peoples air pressure (when that's all they come in for!). In most owners manuals ,to this day , it still states to check fluid levels and tire pressures at each fill up. Whatever happened to OWNER RESPONSIBILITY? IF it's so simple , that we should do it for free , then why isn't it simple enough for the owner? This IS just my opinion.
as further information on repairs to the systems,specifically the sensors in the tires,i was told by a reliable source that the feds mandated that the batteries in the sensors (which are non-replaceable) were to last 8 years but we are starting to see them fail,not all at once but one at a time...not an cheap repair with sensors 85 to 170 or more each plus the labor to take the tire off the rim and also on some models of cars,reprogramming the vehicles computer to recognize the new sensor and what position it is at....