Condition 2

WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.

Before the ECM can report DTC P2237 failed, DTCs P0101, P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336 and P0338 must run and pass.
The ignition 1 voltage is between 10.7-18 volts.
The engine is operating in Closed Loop.
The HO2S heater is at operating temperature.
The ECM detects the internal HO2S signal voltage is between 1.48-1.52 volts.
The ECM is commanding the lambda rich and then lean periodically with a change of more than 2 percent.
DTC P2237 runs continuously once the above conditions are met for more than 1.5 seconds.