Not assigned in the generic OBD-II standard - if your scan tool shows this code, it is manufacturer-specific; verify the meaning in your make's service information

C0131 (master cylinder pressure sensor) on GM trucks indicates the internal pressure sensor in the ABS hydraulic unit is out of range. This sensor is not serviceable separately -- the whole EBCM/hydraulic unit must be replaced or rebuilt. Before replacing, verify brake fluid level is correct and that there are no air bubbles in the system. A proper ABS bleed after any brake work can prevent C0131. Note: this module has to be coded to the vehicle with a factory-level scan tool after installation. Budget for that step, or have a shop supply and code the part.

Escalade C0131 often appears together with soft pedal or uneven brake response. The internal pressure sensor has drifted out of calibration. GM did not release a calibration procedure -- EBCM replacement is the official fix. Remanufactured units run ~$300. After install, perform the ABS automated bleed and the steering angle sensor relearn. Note: this module has to be coded to the vehicle with a factory-level scan tool after installation. Budget for that step, or have a shop supply and code the part.

G6 and Malibu C0131 sometimes clear by performing a proper scan-tool ABS bleed. Air trapped at the master cylinder port can fool the pressure sensor. If bleeding does not clear it, the EBCM is the next step. Always road-test after ABS work -- a truck that logged C0131 should have its brake performance verified before returning to service. Note: this module has to be coded to the vehicle with a factory-level scan tool after installation. Budget for that step, or have a shop supply and code the part.