An optical engine includes a fiber joint, a fiber pad, and a photoelectric module. A hot air plenum is provided along a sidewall of the cart in the hot chamber, and a cold air plenum is provided along a sidewall of the cold chamber. The sides, the front end and the rear end each define a bottom wall thereof, thereby around the central cavity. An outer surface of the sleeve structure comprises a plurality of circumferentially spaced gage pads extending thereover and may comprise a plurality of breaker flats. In the sleep mode, detection of the wheel condition may be suspended or performed less frequently than as the active mode.