Warning lights on your dash shouldn’t be ignored. They’re there to alert you when some aspect of your vehicle needs attention, typically in an attempt to protect the vehicle and/or its passengers. But one warning that was added to dashboards in recent years could use some clarification: Tire Pressure Monitoring System (TPMS) light.
The TPMS light is not required by law to illuminate until your tires are significantly underinflated, and the sensor’s sensitivity may depend on the make and model of your vehicle.
Every vehicle in the 2008 model year or newer (and some 2006 and 2007 models) boasts the TPMS as standard equipment, according to Edmunds, because of the Transportation Recall Enhancement, Accountability, and Documentation Act implemented in 2000.
Government regulations do not require the TPMS warning light to illuminate until a tire is 25 percent below the tire pressure recommended by the vehicle manufacturer. The recommended pressure can be found on a placard on the driver’s-side door jamb. If your recommended pressure is the common 32 pounds per square inch (psi), the TPMS is not required to illuminate until a tire is 8 psi low.
Eight psi can mean the difference between a tire that successfully resists deep water and one that literally surfs on top of a miniature wave. Lower tire pressure can increase your chances of hydoplaning, according to TireRack.com. On dry roads, such a pressure change can be the difference between avoiding an accident and becoming part of the pileup. It’s also enough to cut thousands of miles from the tread’s life.
“The TPMS regulations were meant to warn drivers that a tire failure is imminent, not to indicate unsafe handling might occur,” says National Highway Traffic Safety Administration (NHTSA) spokesman Eric Bolton.
During my time as a driving safety instructor, I have personally ridden in the passenger seat with hundreds of average drivers while they negotiated a wet track with both properly inflated and underinflated tires. Each driver got four laps to familiarize themselves with the course and to get the feel of the vehicle with its tires set to the vehicle manufacturer’s recommended pressure. The driver then got behind the wheel of an otherwise identical car with the rear tire pressure reduced by roughly 20 percent.
With very rare exceptions, these regular drivers felt a significant loss of grip, often by the first turn. (The exceptions were drivers who didn’t go fast enough to provoke the difference.) Quite a few drivers spun out on the third turn, a fairly gentle 30-mph right-hander. Some made the riding instructor carsick as they fought — and lost — a fishtailing car. If the front tires were underinflated, the car would plow straight off the course.
If you see a symbol that is supposed to look like a cross-section of a tire with an exclamation point in the center light up on your dashboard, take immediate action by stopping and filling your tires as soon as possible.
TPMS warnings can be confusing. For example, in the winter, a warning nay not appear as the car is started in a warm garage. After a few moments in the cold it will illuminate, and then disappear. The warning will be there to greet you after your car has spent the day in a cold parking lot, and perhaps disappear on the way home. The root cause: Your tires are underinflated to near the TPMS threshold. A 10-degree difference in ambient temperature can change tire pressure by 1-2 psi, according to Goodyear.
Another variable: Tire-pressure gauges, even expensive ones, can be inaccurate. I’ve seen a swing of 6 psi between the most optimistic and severely pessimistic gauges. Quick tip: The local tire store may allow you to calibrate your gauge.
To reduce the frequency of warning lights and potentially improve hydroplaning resistance, you can set your tires three psi above the door placard, says Edmunds.
Regardless of conditions, properly inflated tires are an important safety measure that should not be overlooked.