Circuit/System Description: P0135
WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.
The ECM determines the temperature by measuring the current flow through the heater. For diagnosis, the ECM monitors the heater current with the engine running. If the ECM detects that the HO2S 1 heater low control circuit current level is not within the calibrated range, DTC P0135 will set for HO2S 1.