SES Light on with a code of P0420 on 2001 Pontiac Montana

SES is on with a code of p0420. I can clear it then it comes back on after a couple of days.

by in Wilmington, OH on April 09, 2009
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2 answers
ANSWER by , April 09, 2009
check out this article on this code and what it mans:
ANSWER by , April 10, 2010
Check for cracks near the o2 sensor near the exhaust manifold.