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TPMS Light Vs Tire Pressure Light
When they drive their vehicle into the shop, many drivers don't know the difference between the tire pressure light and the TPMS light. Customers frequently confuse the two, telling the service mechanic, "One of the symbols lit up on my dash, and I assume it's the tire pressure." Knowing which indicator is lighting up can make the difference between getting straight to the problem and ending up wasting a lot of time on troubleshooting to find the problem.
The TPMS Indicator
When there is a clear problem with the TPMS as a system, this indicator illuminates and remains illuminated. The TPMS stops monitoring tire pressures and turns off. If this indication or message appears, use the HDS to verify the TPMS control unit for set TPMS DTCs and troubleshoot as needed.
However, experienced drivers know that a TPMS light coming on is not always a cause of concern. For instance, when traveling at high altitudes, many drivers tend to experience their car tires change pressure quicker than usual and more unevenly. This is mainly because the 30psi gauge at 5000 feet will always get you less total air in the tire than the 30psi gauge pressure that's close to sea level.
This is often a cause of alarm for many new drivers who tow a trailer and witness the rear tires heating up more than the front tires due to the trailer's load. This is where many drivers tend to create better balance by inflating the rear tires 1 psi higher, which will almost always get you a differential of around 3psi, which results in the TPMS light coming on.
This is the reason why the TPMS system in your vehicle cannot replace manual checking of the tire pressure, which should be done at least once a month, depending on how many times you take your car out for long drives.
Tire Pressure Light
When the tire pressure is between 18 and 25% (depending on the model and tire combination) below the recommended number specified on the driver's doorjamb sticker, this indication (a tire cross-section with an exclamation point in the center) lights up. Some newer model vehicles are also equipped with a "check tire pressure" message that comes on when there is an issue with the tire pressure. This is the recommended cold inflation value at all times.
Consider this sign to be the tire's low-fuel indicator. If the RO states this is the indication that came on, simply compare the tire pressure to the suggested number and inflate to the right pressure.
When checking tire pressures, make sure you use an accurate tire pressure gauge and do it when the tires are cool. Because accuracy can be a problem with these gauges, it's a good idea to calibrate your tire pressure gauge on a regular basis.
Common TPMS Issues
A malfunctioning TPMS sensor in a car isn't unheard of. It should be noted that there may be a problem with the TPMS sensor in your car if the light either remains on even after inflating the tires back to normal or if the light remains illuminated or starts to flash after the tires have been checked and inflated properly.
"Test Before Touch" is one of the diagnostic mantras advocated by today's service specialists. This basically means you should always use a TPMS tool to activate and analyze the response signal from each tire pressure sensor in each wheel before doing anything else. This is advantageous in two ways. It will either show if the sensor is capable of measuring the tire pressure or whether it is creating a signal without the right reading.
Calibrating your tire pressure gauge is crucial to getting an accurate reading. The pressures on the cheap spring-loaded stick-style tire gauges can vary by as much as 5 psi. They are the most precise since many new digital gauges have a self-calibrating system that accounts for fluctuations in ambient air temperature.
By using a gauge, you can verify the actual pressure in the tire. You should get a reading of 32 psi when you check the pressure using a gauge if the pressure number reported on your TPMS tool from a sensor is 32 psi. If you find a TPMS sensor that isn't working or reading correctly, it's natural to think that the sensor is the root of the problem and that replacing it would fix it. It almost always does.
However, unless you evaluate the rest of the system, you won't know if a damaged sensor is the only problem affecting the system's performance. If all of the sensors appear to be functioning properly and all of the tires are properly inflated, but the TPMS warning light remains illuminated or flashes, you'll need to investigate further if you want to get to the root cause of the problem.
Now that you know all there is to know about the TPMS light vs tire pressure light, you will be able to make a better decision when it comes to identifying the problem the next time one or the other light comes on while you are driving.
About The Author
I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.Read More About Charles Redding