rich condition in step 104 in step 106 the controller 12 initiates operation of the pump 30 and opening of the valve 32 to supply air into the exhaust manifold 22 in this manner o 2 is injected into the rich exhaust stream to create a lean exhaust stream in step 108 the inlet o 2 sensor 26 is checked by the controller 12 to determine whether the inlet o 2 sensor 26 has detected the created lean condition if the inlet o 2 sensor 26 does not detect the lean condition a fault is signaled in step 110 to indicate that the secondary air injector 16 is not functioning properly if the inlet o 2 sensor 26 does detect the lean condition a signal indicates that the secondary air injector 16 is functioning properly in step 111 and control continues with step 112 in step 112 the controller 12 determines whether the outlet o 2 sensor 28 has yet detected the lean condition if the outlet o 2 sensor 28 has not detected the lean condition control loops until the outlet o 2 sensor 28 detects the lean condition once the outlet o 2 sensor 28 detects the lean.