P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1.
The sensor is monitered for switching, it fails to switch when circuit or fuel excedes a calibrated limit.
Here the possible causes
- short to VPWR is harness
- Water in harness
- short/open circuit
- corrison or bad wiring
- damaged O2 sensor
- damaged PCM
- excessive fuel pressure
- leaking injectors
- leaking fuel pressure regulator
- car is almost out of fuel
- air leaks after MAF
- vacuum leak
- PCV system
- engine oil dipstick not seated
- EGR valve gasket leaking
- stuck EGR valve
- leaking diaphram or EVR
- oil overfilled
- cam timing is off
- cylinder compression
- exhaust leak near the O2 sensor
hope that helps
