DTC P0131 Or DTC P0132: Condition

WARNING: This page is about a different car, the 2002 Suzuki Esteem. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when Heated Oxygen Sensor (HO2S) No. 1 output voltage does not vary from less than 0.3 volt to more than 0.6 volt when vehicle is operating after reaching normal operating temperature. This circuit is monitored once per drive cycle. MIL is illuminated when Engine Control Module (ECM) detects malfunction during 2 consecutive drive cycles. Possible causes are:

HO2S No. 1 malfunction.
Open or short in circuits between HO2S No. 1 and ECM.
Low fuel level.