P0031 and P0037 Error Codes - 2003 Nissan Altima O2 Sensor Heater Circuit Issues
My check engine light is on, and the scan tool detected codes P0031 and P0037. These relate to the oxygen (O2) sensor heater circuits for Bank 1 Sensor 1 and Bank 1 Sensor 2. I replaced both sensors, but the codes returned immediately after. I'm confused as to why new sensors are still triggering these error codes. The issue seems to be related to the heater circuit rather than the sensor itself.
The P0031 and P0037 codes indicate issues with the O2 sensor heater circuits. If the heater element is functioning properly, check for a consistent 12V power supply and proper ground connection in the circuit. If the heater circuit is fused separately, inspect the fuse—blown fuses are a common cause of these errors.