The major difference between LSU 4.9 and 4.2 is that LSU 4.9 uses the reference pumping-current, while LSU 4.2 uses the reference air. What does this mean? Let’s read this true story the auto industries: when Bosch first designed a wideband oxygen sensor, a reference air cell was used to provide a reference of stoic AFR. -The major difference between LSU 4.9 and 4.2 is that LSU 4.9 uses the reference pumping-current, while LSU 4.2 uses the reference air. What does this mean? Let’s read this true story　the auto industries: when Bosch first designed a wideband oxygen sensor, a reference air cell was used to provide a reference of stoic AFR.