P0421- Warm up catalyst below threshold (Bank 1)- where is this located? on 2004 Hyundai Elantra

I have a 4 cyc single exhaust 2004 Hyundai- I have one 02 sensor on top of the exhaust manifold; another one just below the flange of the exhaust manifold where the exhaust pipe connects to the exhaust manifold.

by in Imperial Beach, CA on November 23, 2012
1 answer
ANSWER by on November 24, 2012
Your warm-up catalytic convertor is in your exhaust manifold