Mercedes has travelled to Austin with fixes for the two reliability problems suffered at Sochi recently.
Nico Rosberg's title chances were effectively destroyed when a small and inexpensive 'O-ring' in the throttle mechanism broke.
It was a tried and tested design, but Auto Motor und Sport reports that Mercedes has reacted by re-designing it anyway.
"We never expected that it would fail," an engineer is quoted as saying.
And even though Lewis Hamilton went on to win in Russia, the pitwall was nervously watching an intermittent 'stalling' problem with his rear wing -- probably caused by chunks of tyre debris sticking to it.
"The wing has been modified in the area of the endplates in order to guarantee stable downforce," correspondent Michael Schmidt reports on Thursday.
Marc Surer, a former F1 driver turned TV pundit, said he expects Hamilton to seal the lid on the drivers' world championship this weekend.
"I think so," he told the German broadcaster Sky. "Unless his car fails.
"Reliability at Mercedes has been a problem lately, with Rosberg suffering not only at the last race but also in Singapore.
"And it always seems to be something different. That is what is unpredictable and difficult for them to control now," Surer added.
Bahrain International Circuit - Winter testing
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