Phillip Potter told Bristol Crown Court he honked the horn to warn people and thought: "I'm dead. This is the end."
Mitzi Steady, four, Robert Parker, 59, Philip Allen, 52, and Stephen Vaughan, 34, died in the crash in Bath in 2015.
Mr Potter, 20, of Dauntsey, Wiltshire, denies a total of 10 charges including causing death by dangerous driving.
He was driving a truck belonging to Grittenham Haulage Ltd. The owner of the firm, Matthew Gordon, 30, also of Dauntsey, denies 14 charges against him.
Peter Wood, 55, from Brinkworth, Wiltshire, a mechanic who carried out safety checks on the truck, denies four charges against him.
Mr Potter said he realised the brakes were not working as soon as he saw a 20mph restriction sign on Lansdown Lane.
He said: "I was really scared. Honking the horn was the only thing I could think of, to warn people that I couldn't stop."
Mr Potter told the court that he could see a little girl running out into the road and tried to swerve the vehicle in order to miss her.
He said: "I didn't know that I had hit her, but had a feeling I had. I didn't feel the impact."
Mr Potter explained that "everything happened so fast" and claimed Mr Gordon said "don't tell the police about the ABS light" immediately following the crash.
Four-year-old Mitzi was one of a number of pedestrians struck by the lorry.
Mr Allen and Mr Vaughan, both from Swansea, and Mr Parker, from Cwmbran, south Wales, were in a car hit by the vehicle.
The case continues.
The driver of a truck which crashed and killed four people described feeling "really scared" when he realised the brakes were not working.