The warning light notifies pilots of a disagreement in the sensors that measure which direction the plane is pointed, a potential sign of a malfunction. This light could have provided critical information to the pilots on two flights that crashed shortly after takeoff in recent months.
Boeing's newest 737 model, the MAX, was grounded worldwide in March following two fatal crashes, one on Lion Air in Indonesia in October and another on Ethiopian Airlines in March, which together killed all 346 on board.
Chief Executive Officer Dennis Muilenburg said on Friday said the company now knows that a chain of events caused both disasters, with erroneous activation of so-called MCAS anti-stall software "a common link" between the two.
A Boeing official in Seattle said on Wednesday the timing of the software upgrade was "100 per cent independent of the timing of the Ethiopian accident," and the company was taking steps to make the anti-stall system "more robust."
Ethiopian and French investigators have pointed to "clear similarities" between the two crashes, which killed 346 people, putting pressure on Boeing and US regulators to come up with an adequate fix. The causes of the crashes are still unknown.
Boeing has been working on a software update to an anti-stall system called MCAS since a Lion Air plane crashed in Indonesia in October, killing all 189 aboard. That effort has become urgent after a second 737 MAX 8 crashed in Ethiopia last week.
The main wreckage and the CVR, one of two so-called black boxes, were not recovered in an initial search. Lion Air said in December it was funding a 38 billion rupiah ($2.64 million) search using the offshore supply ship MPV Everest.