The AEM X-Series Wideband Gauge and X-Series Inline Controller support the 4.9LSU sensor and utilize both factory calibration resistor and free-air calibration methods, providing precise factory calibration when the sensor is new and allowing free-air calibration to help correct drift as the sensor ages. AEM Wideband UEGO (Universal Exhaust Gas Oxygen) Controllers accurately monitor engine Air/Fuel Ratio (AFR), providing critical data for tuning. Running rich can reduce power, while running too lean may cause serious engine damage. Monitoring AFR allows tuning adjustments to optimize power and efficiency. The UEGO sensor connector should not be modified because it contains a laser-etched calibrated resistor specifically matched to the sensor; modification will invalidate the sensor output. Independent testing by 360° Product Testing, reported August 31, 2015, against 17 competitor wideband UEGO controllers found the AEM X-Series Inline and X-Series Wideband UEGO AFR Gauge with 4.9LSU sensors recorded the fastest response times. Wideband UEGO sensors are wear items affected by leaded fuels, automotive fluids, particulates, mechanical or thermal shock, and unheated exposure to exhaust. Free-air calibration may correct sensor drift, but replacement as part of regular vehicle maintenance is recommended. Follow the instruction manual when performing free-air calibration. AFR ranges: 0-5V Gasoline 8.5:1-18.0:1; CANbus Gasoline 8.0:1-20.0:1; CANbus Lambda .55-2.00; 0-5V Lambda .58-1.23; 0-5V E85 5.7:1-12.0:1; Ethanol 5.2:1-11.0:1; Methanol 3.75:1-8.0:1.