Speed Sensor
The Vehicle Speed Sensor (VSS) buffer amplifier supplies vehicle speed information to control module. Optic head portion of VSS is located in speedometer frame. See Fig 2 . A reflective blade is attached to speedometer cable/head assembly. Reflective blade spins like a propeller, with its blades passing through a light beam from an LED in optic head.
As each blade enters LED light beam, light is reflected back to a photocell in optic head causing a low power speed signal to be sent to buffer for amplification and signal conditioning. This amplified signal is then sent to control module. See Fig 2 .