i have a 3 page description on how to check the OXS from the engine compartment. it involves removing the air filter cover to get at the OXS signal lead whereby you measure the current on an idling engine. the allowable range is 0.5 to 3.0 amps. looks like a pretty straight forward procedure. "if specified value is not obtained replace OXS". yes, i can fax those pages to you... eliot