The initial investigation into the October Lion Air crash in Indonesia, which killed all 189 people on board, found that an "angle of attack" (AOA) sensor failed but continued to transmit erroneous information to the MCAS.
This comes after the WSJ reported on Friday that the plane's anti-stall system, created to automatically correct the jet's direction if a sensor detects the aircraft is tilting up, had been activated before the Boeing 737 MAX 8 crash, which killed all 157 people on board.
Norwegian, which has 18 737 MAX 8 in its fleet and is scheduled to take delivery of dozens more in the coming months and years, said last month it would seek compensation from Boeing over the grounding.
Families in 35 nations were left bereaved when the plane went down just minutes after takeoff from the highland capital on a flight south to neighbouring Kenya, crashing into a field.
First Officer Ahmed Nur Mohammed contacted the control tower and in a crackling transmission reported a "flight control problem", according to the newspaper, which cited people close to the ongoing investigation.
A source with knowledge of the investigation has said an anti-stalling system, the maneuvering characteristics augmentation system (MCAS), was activated shortly before the crash.
Authorities in Ethiopia have already said there are "clear similarities" between the Lion Air incident and the Ethiopian Airlines crash. This was previously an optional safety feature.
U.S. Senator Chuck Schumer wants Boeing to be removed from a Federal Aviation Administration rulemaking committee as investigations deepen into both the company and regulator's role in two deadline airline crashes.
Boeing and the FAA declined to comment to AFP.
American-based CNBC published that the plane flew out of the sky after the pilot was unable to regain control.
Earlier this week, Boeing said that the upgrades were not an admission that the system had caused the crashes.
Boeing has tried to restore its battered reputation, while continuing to insist the 737 Max is safe.