Conditions for Setting the DTC: P0139
WARNING: This page is about a different car, the 2008 Suzuki Swift +, 2008 Pontiac Wave, and 2008 Chevrolet Aveo. However, it is still accessible from the selected car via links, so may be relevant.
The ECM detects that the HO2S 2 response time is greater than 25 seconds after DTC P0420 runs.