TPMS – Making sure the light comes on when it’s supposed to!, from AutoPro Workshop.
“The light wasn’t on when I got here!”
Your customer is adamant that the funny looking yellow warning light now brightly illuminated on his instrument panel was not “on” when he brought the car in. You know, the one that looks like a tire cutaway with an exclamation point in the middle of it? That’s the warning light for the Tire Pressure Monitoring System (TPMS) and if you’ve recently performed some type of tire-related service or repair, odds are you forgot to tell the TPMS controller that you made some changes.
The first TPMS systems were a bit more forgiving than their more modern cousins, relying on existing Antilock Braking System (ABS) sensors to monitor tire pressure. These early systems inferred the tire pressure by plugging wheel speed data into a complex algorithm to monitor tire circumference. A low tire has a smaller circumference and will rotate faster than a properly inflated tire of the same type and size. These systems had to be placed in a “learn” mode whenever tire rotations or replacements were performed. Tire pressures would be corrected and then the vehicle would be driven in order for the system to establish an accurate baseline.