The P2-26 refers to the connector pin on the operator control board. P2-26 is for the FaST side brush valve (solenoid valve to turn on the FaST soap pack to the side brush). From what you've described, the P2-26 code that comes up after you run the self-test is indicating a problem with that particular function. This is a separate issue from the engine stalling.
On that note, the engine stalling could be an issue with the connection to the the ECM or a faulty ECM. Get a wire schematic for the ECM and M30 to help guide you through the many wires to the ECM. Best of luck!