how to fix po128 code on this van on 2002 GMC Safari

I am trying to determine how to diagnose a PO128 error code on a 2002 GMC Safari. I would appreciate any info anyone might have on this

by in Baldwinsville, NY on December 17, 2012
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1 answer 1 comment
ANSWER by , December 17, 2012
Here's the obd code: I would suggest if the coolant level and strength are good, it is probably a bad thermostat that needs replaced.
COMMENT by , December 18, 2012
thank you.. I will try that