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.Google+
Car Problem Reports
Chevrolet Express 3500 Check Engine Light Due to Restricted Secondary Air Injection Check Valves
Chevrolet Express 3500 Problem
Exhaust & Emissions Affected: Gasoline
Average Mileage: 48,000 mi (29,000 mi - 67,000 mi)
Visitor, 2005 Chevrolet Express 3500
check engine light came out when it was still 210,344 miles - since then, i have replaced the o2 sensor twice but the light keeps coming back. engine runs well.