2008 GMC Yukon engine problems

Tl* the contact owns a 2008 GMC yukon. While driving at approximately 25 MPH and approaching a stop sign, the brake pedal was depressed but the vehicle did not stop. The accelerator pedal was depressed, but the vehicle did not accelerate. Another vehicle crashed into the front passenger of the contact's vehicle. The air bags did not deploy. The contact suffered a concussion and the pregnant front passenger sustained back injuries and received medical attention. A police report was filed.

The car flashes reduced engine power, stabilitrack off and the car can barely go 30 MPH. The engine runs very rough when it is doing this also. My code scanner displays code 641 which is open 5volt reference on bank 1. It does this more when the weather outside is warmer or the car has been sitting still while running. On more than one occasion it has happened while pulling out into traffic causing near misses and other times while driving down the highway. Just yesterday it did it 20 times in a four mile stretch.