I've been chasing this demon for months. Fault code is P0491 (secondary air pump flow bank 1). pump, valve, vacuum hose and solenoid are all good. Tried the seafoam trick (remove secondary air valve pour in 2 Oz. seafoam, replace valve then cold start) This confirmed the fault code because white smoke billowed out of the bank 2 side tailpipe but not the bank 1 side. I spotted 2 non-return valves (part no. 11121706921 one for each side) and I suspect that might be the problem.
Can anyone confirm that these non-return valves are part of the secondary air pump system?


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