TPMS Systems and How to fix a TPMS Light On
What is TPMS
A tire pressure monitoring system (TPMS) is an electronic system that monitors the air pressure inside your tires. When there’s a problem with tire air pressure you’ll see a TPMS light on on your dash. There are several types of monitoring systems; direct and indirect. Direct TPMS uses a sensor mounted near the tire valve stem or strapped to the inside of the wheel. The sensor contains a battery, accelerometer, pressure sensor, and a radio transmitter that communicates with a receiver in the vehicle. Indirect systems, on the other hand, don’t use sensors. The ABS braking system calculates tire pressure by comparing the revolutions of each tire to one another. A tire that’s low on air will have a different circumference and thus a different rate of revolution.
TPMS is required on all light-duty vehicles made after the 2007 model year and must monitor the pressure on four driving wheels. The system must detect and alert the driver when pressure falls to 25% less than the manufacturer-recommended pressure, although carmakers are allowed to set their sensor if pressure drops less than the 25%. Plus, the system must warn the driver if there is a system malfunction. Finally, the system must illuminate the visual indicator to act as a “bulb check.”
How a TPMS sensor works
Most of the time, the TPMS sensor is in sleep mode. If the vehicle isn’t moving, the transmitter sends a signal once each hour. It wakes up when the vehicle is in motion and sensor a brief report to the TPMS receiver every 30 to 60 seconds once the vehicle reaches 15-20 MPH.
Why TPMS is required
Low tire pressure increases rolling resistance which decreases fuel mileage. Worse yet, low tire pressure causes excessive tread and sidewall flex which increases heat buildup. Heat buildup dramatically reduces the life of the rubber and internal belts and can cause premature and sudden tire failure. Studies show that nearly 250,000 accidents every year are caused by underinflated tires and that 75% of all roadside flats are preceded by a slow leak and under-inflation.
How to reset a TPMS sensor
If a tire is low and you’ve received a dashboard notice, simply fill the tire with air and drive the vehicle. After a while, the sensor should report to the receiver and the warning light should go out. If it doesn’t refer to your owner’s manual for instructions on how to perform a manual reset.
Be aware that some carmakers install TPMS sensors on the spare tire. So, if you’ve filled your four driving tires and still have a TPMS light on, double-check the pressure in the spare tire before assuming you’ve got a problem.
The most common problem with TPMS light on condition is a change in ambient temperature. Tires must be checked and filled when the tire is cold. If you drive the vehicle and fill the tires when they’re warm, the pressure will drop as the tire cools and that can cause a TPMS light on condition. Generally, you’ll see a 1-psi drop in tire pressure for every 10° F drop in ambient temperature. So you’ll see the TPMS light come on more in late Fall as the outside temperatures drop and internal tire pressure drops along with the outside temperature.
Other things to know about TPMS sensors
On some vehicles, the metal valve stem cap is part of the radio antenna. If you lose the cap, the TPMS sensor may lose contact with the receiver.
Early sensors were made with different metals, which was a huge mistake on the part of the carmakers. As a result, galvanic corrosion can set it and eat away at the metal portions of the valve stem. If you try to remove the metal cap, you can actually break off the valve stem. That’s why many shop warn you they won’t be responsible for broken TPMS sensors.
Battery life is 7-10 years and the battery is not replaceable. When the battery fails, you must replace the entire TPMS sensor.
You do not need to go to the dealer for a new TPMS sensor. Any tire shop can replace and program a TPMS sensor for far less than a dealer.
Shops are prohibited by law from disabling a TPMS system. Don’t ask them to disable your TPMS system.
©, 2020 Rick Muscoplat
Posted on by Rick Muscoplat