P1131 Lack of H02S Bank 1 Sensor 1 Fuel trim at limit
This code condition is for the the 02 sensor at Bank 1, being sensor 1 this is the upstream 02 sensor. What set this code is either the 02 sensor is not properly connected or the 02 sensor has degraded,
What this code stands for is that the 02 sensor on Bank 1 has stoppped switchng, what can cause the 02 sensor from switching is a vacuum leak that will cause a lean condition, The 02 sensor not properly connected, or a failed 02 sensor
A good 02 sensor will switch from lean to rich its voltage would go from 0.250 volts to 0.850 volts which is the reflection of a good working engine and being in fuel control.