u1900 is a generic fault when there is a break down in communications with the CAN network ( controlled area network) in english and straight forward terms the ECU is not receiving a clear communication from anything from a sensor to a electrical fault.
usually you should get another code with a fault with this, so it may be worth taking to the garage and getting it onto a diagnostic kit to retrieve the code.
Considering the make and particular vehicle u1900 code has often been thrown up (with the same symptoms as you describe) as an ABS sensor fault.