2003 Hyundai Santa Fe OBD11 Code P0421

[quote:423a209e86="Dale Blackwell"]Computer problem
2003 Hyundai Santa Fe 4 cyl Two Wheel Drive Automatic 72000 miles
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OBD Code Po421
Changed the catalytic converter recently.
Engine would hardly go over 15 mph.
Repaired broken valve #2 cylinder.
New valve job.
New rebuilt transmission.
Suspect Vacuum leak or oxygen sensor[/quote:423a209e86]

Ok, so vehicle is running fine now and only need info on code?

Code Definition:

P0421 - Warm Up Catalyst Efficiency Below Threshold