One or both secondary air injection check valves may become restricted causing poor air flow resulting in illumination of the Check Engine Light. It is often recommend to replace both check valves even if a fault code is set for only one bank of cylinders. Replacing only one valve may result in a return trip to the repair shop.
Car Problem Reports
GMC Sierra 2500 HD Check Engine Light Due to Restricted Secondary Air Injection Check Valves
GMC Sierra 2500 HD Problem
Exhaust & Emissions Affected: Gasoline
Visitor, 2007 GMC Sierra 2500 HD, 30,000 mi
light was always on. Dealers blamed it on becuase the truck was lifted. Dealers blamed in on after market pipes. Put stock air filter back on still had problems. A friend put back on the Air Raid filter, he seemed to tighten it real tight, over a year now and no light problems. Pass Californias new stupid SMOG in 2011. Problem started at 30,000 but would go away for a few months, then act up again. at about 90000 after Air Raid put back on it stopped.