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P0421 Diagnostic Trouble Code Discussion for May 2004

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2000 Audi A6 Quattro 2.7L MIL Lamp on VIN: WAUED54BXY
P0421: warm up cat bank1/ efficiency below threshold. Hi, This audi has had secondary air injection codes for some time. The system was tested for operation and pump runs, it was replaced because of noise. Both valves on the rear of the heads were removed, cleaned, tested. The vacuum hoses are all intact. The euc...
May 27, 2004