Red Bull Racing says the engine change undertaken by Honda on Alex Albon's car on Thursday was a mere "precautionary" measure.
Albon's first day of pre-season testing was hampered by a lengthy stay in the Red Bull pit box.
Head of Race Engineering Guillaume Rocquelin provided some insight into the reason for the halt and the subsequent engine swap.
"We had another very productive day with the RB16 and although we didn’t complete quite as many laps as Wednesday, we once again got through all of the test items on the list," said the Red Bull engineer.
"We did have a small issue just before lunch when the Honda guys noticed something in the data and we, therefore, elected to perform a precautionary engine change.
"They’ve done a thorough check and there are no problems, so the original PU will be back in the car on Friday."
Despite the engine change, Albon still managed to tack on a healthy 134 laps and the fourth fastest time of the day.
"It was a good first day with the RB16," said the British-Thai racer.
"After Max’s running yesterday, we carried on the work today and tried a few things that he tried. Comments wise we were very similar which is always positive.
"We lost some time in the middle of the day due to an investigation on the power unit but other than that it was pretty smooth.
"Over the winter we have addressed some of the areas where we felt we were struggling, and I felt pretty comfortable in the car straight away.
"It’s always nice to get back in the car and you always feel it on your first day back but it was good out there and the car is feeling strong."
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