Both Technician A & B are correct. TPMS are divided into two different types – direct (dTPMS) and indirect (iTPMS). Direct TPMS employ pressure sensors on each wheel, whether internal or external. The sensors measure the tire pressure in each tire and report it to the vehicle's instrument. Indirect TPMS do not use physical pressure sensors but measure air pressures by monitoring individual wheel rotational speeds and other signals available outside of the tire itself.
