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P0421 Diagnostic Trouble Code Discussion for February 2008

Warmup Catalyst Efficiency Low (Bank 1)

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Trouble Ticket Help Requests for DTC P0421
Help Request Posted
2001 Hyundai Santa Fe LX 2.7L MIL Lamp on VIN: 3GH4956L13
P0421: Warmup Catalyst Efficiency Below Normal (Bank 1). After verifying code with scope, I replaced cat with reman unit along with exhaust manifold for cracks and the B1S1 O2 because it was seized in the manifold. Code reappeared in pending and after checking Mode 6 for cat test found it was failing worse than the ...
February 07, 2008
2001 Volkswagen Passat GLX 2.8L MIL Lamp on VIN: WVWBH63B21
P0421: Warm up cat efficiency below threshold bank 1. This car came back with cat efficiency codes after about a week and we suspect cat but wanted to post to see if any one had any ideas. I am nervous about changing the cat and having light come back and some other problem. Is this a common problem? VW guys, do ...
February 12, 2008