Every fleet strives to keep its vehicles on the road and keep their drivers safe when they are behind the wheel. Over the years, advancements in technology have allowed owners and maintenance professionals to better accomplish those goals by providing them the means to monitor their trucks, assess the effectiveness of their vehicles, address repairs both great and small, as well as protect their fleet’s bottom line.
In the Technological Recall Enhancement Accountability and Documentation (TREAD) Act of 2000, Congress called for the National Highway Traffic Safety Administration (NHTSA) to craft a rule requiring all new motor vehicles to be equipped with a warning system to notify a driver of an issue related to tire pressure. Tire pressure monitoring systems (TPMS) were the end result of that legislation and, by Sept. 1, 2007, 100 percent of new vehicles brought to market were equipped with TPMS.
A TPMS warning serves to inform a vehicle’s operator of tire underinflation or a system malfunction, and seeks to compel the driver to stop and investigate the cause of the alert. There are two types: indirect and direct.
An indirect TPMS often utilizes wheel speed sensors to measure the rate of revolution each of the vehicle’s wheels is making. The data collected is then analyzed by an onboard computer to determine the approximate sizes of the tires. If one or more wheels spin faster than it should, the operator is warned that the tire is likely underinflated. This warning is done via the dashboard display or driver information center (the digital display where the driver can view the odometer, etc.)
Direct TPMS relies on pressure monitoring sensors within each of the vehicle’s tires that constantly measures specific pressure levels. The sensors collect data and transmit it to a centralized control module via radio frequency. If a tire is underinflated, the driver is notified via an illuminated indicator light on the dashboard display or driver information center.
“If the light is on, there is an issue, period,” says Michael Flink, national sales manager – commercial, Autel North America, a provider of TPMS and other vehicle diagnostic equipment (www.autel.us). “The trick is to determine what is the true issue, how to resolve it and how to get the system to recognize you've resolved it.”
According to Eri Muca, director of sales, Alligator North America, a manufacturer of TPMS sensors, valves, service kits and programming tools (www.alligatorna.com), a solid, unblinking TPMS light often indicates a pressure error, while a blinking light usually means one or more TPMS sensors are not communicating with the vehicle.
“It’s giving the message that something is not working properly,” adds Muca. “TPMS has been designed for vehicles as a safety item, so if this system is not properly working, the driver would have a very difficult time understanding if he or she was driving with an underinflated tire or not.”
VISUAL INSPECTION
If a driver receives a TPMS warning, the first step he or she should take to determine its cause is a simple visual inspection. According to Autel’s Flink, if the vehicle's system provides a warning via dashboard display or driver information center, the operator should attempt to discern which tire or tires, if any, are to blame. Then, he or she should verify the pressure in the tires immediately.
“Anytime you see a TPMS light go on and it is solid, you must stop and check the tires,” says Muca of Alligator, adding that a vehicle’s TPMS is designed to notify a driver when a tire is underinflated by 25 percent. In addition, he says, underinflated tires can extend vehicle braking distance and, in some cases, lead to tire failure.
“Don't forget to include checking the spare if equipped,” says Flink. “Remember, if someone previously the rotated tires and didn't do a relearn (reset the sensors), the vehicle may indicate the wrong tire location is low. If a spare was included in the rotation, and the system only follows four tires, then the spare may be the one setting off the light.”
CAUSE AND EFFECT
While the most obvious cause of a warning is an underinflated tire, there are occasions when the TPMS is malfunctioning because a sensor contained in one of the tires is too weak to transmit. As a result, the system is more or less is operating under the assumption that there are only three wheels on the vehicle. This is often because a sensor was replaced without “teaching” the vehicle its new identification number, or the sensor was programmed incorrectly.
A damaged or ineffective transponder may also be the cause as it would not be able to send a signal from the TPMS sensor to the control module. According to Autel’s Flink, this is an irregular occurrence, but it can take place if a vehicle was used off the road, operated in rural settings or had a tire come apart.
Once the underinflated tire is addressed or the malfunctioning sensor is replaced, the potential still exists for the TPMS to warn the driver of a problem. It is not uncommon to assume a defective replacement is to blame, but that may be an incorrect diagnosis.
Flink suggests that once the initial cause of the TPMS warning has been identified and resolved, the relearn procedure for the vehicle must be initiated. Since the TPMS sensors don’t transmit constantly, but rather only when they see a problem, performing a relearn process forces them to check in with the control module. “Now the (module) knows the latest results,” he says.
RELEARN PROCEDURE
One significant hurdle for fleet maintenance managers to overcome as it relates to TPMS systems is that there is no standard relearn procedure for all vehicles. According to Flink of Autel, some allow for a manual process, such as key fob buttons or dashboard resets, while others require the use of a tool.
“When these types of systems go into relearn, they basically open their ‘ears’ to any sensor transmitting on their frequency,” he says. “Typically, the vehicle then thinks the first signal is left front, then right front, etc. When complete, it goes back into locked mode and only reads its own sensors. You get the system to see or hear the sensor by activating it.”
Two ways Flink recommends activating a sensor are by letting air out of one of the vehicle’s tires until the pressure is very low and a warning is sent out, or by employing a TPMS tool to wake up the sensor. In some situations, there is reason to be concerned about more than one vehicle in a shop relearning at the same time, which could cause the TPMS on one vehicle to confuse its sensors with those located in the other’s tires.
To prevent such an issue, maintenance professionals can read the sensors with a tool and then enter the identification numbers into the TPMS controller using a diagnostic tool through the OBD-II port.
“Some vehicles also have a reset button or switch you have to press or activate to start its relearn,” says Flink. “Often then the relearn is done by filling the tires to proper pressure and performing a drive of some amount of minutes above a certain speed. Finally, some vehicles require you perform a drive and self-relearn.”
Whatever the vehicle’s make is, certain steps must be followed to allow the TPMS to recognize an issue has been identified and fixed properly. Then, and only then, will the light turn off and the driver can safely operate the vehicle.
“On those vehicles with codes, you may also have to clear them from the controller to extinguish the light,” he adds.
EFFICIENT AND EFFECTIVE
In addition to ensuring driver safety and keeping vehicles on the road, TPMS also helps vehicles operate efficiently and effectively by helping save on fuel costs and tire wear through helping maintain tire inflation pressures. Fleets can save money and improve uptime simply by better understanding TPMS and embracing best practices as they relate to dealing with warnings and maintenance. By doing so, they will avoid unplanned breakdowns and maintenance issues, as well as vehicle downtime, which leads to greater profit and productivity.
