Diagnosing TPMS Concerns

The TPMS light is one of the most common dash lights you will deal with. The key is knowing the difference between a low tire warning and a system fault — because the diagnosis and the fix are completely different. A solid light means a tire is low. A flashing light means the system itself has a problem.

A solid TPMS light means at least one tire is 25 percent or more below the placard pressure. Check all four tires plus the spare — some vehicles monitor the spare. Inflate to the door placard specification. Drive for a few minutes. The light should turn off. If it does not turn off after driving at least 10 minutes above 25 mph, recheck all pressures. If all pressures are correct and the light stays on, move to step 2.

Connect the scan tool and read codes from the TPMS module or BCM depending on the vehicle. The codes will tell you which sensor is not communicating or which sensor is reading an implausible value. Common codes: sensor not responding, sensor battery low, sensor ID not programmed, and communication timeout. If the code points to a specific wheel position, you know which sensor to investigate.

Use a TPMS activation tool — a handheld device that sends a low-frequency signal to wake up the sensor inside the tire. Hold the tool near the valve stem and activate it. A functioning sensor will respond by transmitting its pressure reading and ID. Most activation tools display the sensor response. If the sensor does not respond, the battery is dead and the sensor needs replacement. Test all four sensors — if one battery is dead, the others are the same age and may fail soon. Inform the customer.

A TPMS light that flashes for 60 to 90 seconds at key-on and then turns solid indicates a system fault, not a low tire. This means the module is not receiving data from one or more sensors. Common causes: a dead sensor battery, a sensor that was not relearned after a tire rotation or tire replacement, a sensor that was damaged during a tire change, or an aftermarket wheel that blocks the sensor signal. If the light started flashing after a tire service, the most likely cause is that the relearn procedure was skipped.

After replacing sensors, rotating tires, or any time the module does not know which sensor is at which position, perform the relearn procedure. The procedure varies by manufacturer. Some require a scan tool to enter each sensor ID into the module for each wheel position. Some require the TPMS activation tool to trigger each sensor in a specific order — left front, right front, right rear, left rear — while the module is in learn mode. Some vehicles self-learn after a reset and a drive cycle at a specific speed. Always look up the exact procedure. A common mistake is assuming all vehicles use the same relearn process — they do not. Getting the sequence wrong or skipping a step means the light stays on and the customer comes back.

When replacing a direct TPMS sensor, make sure the new sensor is compatible with the vehicle. Aftermarket programmable sensors — sometimes called universal or cloneable sensors — must be programmed with the correct protocol for the vehicle before installation. OE sensors are vehicle-specific and do not require programming. Always replace the valve stem seal and nut when replacing a sensor — reusing the old hardware leads to air leaks. Torque the valve stem nut to the sensor manufacturer specification — overtightening cracks the aluminum valve stem and causes a leak that is very hard to find.