2006 chevrolet cobalt ss 2.4L non supercharged troubleshoot "code PO128"?

[Matthew Tait]

i was wondering if someone could help me with this code i drove to van and as i was comin back home my engine light came on and my fan stayed on constantly, on my information center the coolant had 3 dash lines across not telling me the engine temp . my engine is running perfectly fine im just wondering what the problem might be im getting annoyed of the fan thanks