Mercedes boss Toto Wolff has labelled Lewis Hamilton's MGU-H failure at the Russian Grand Prix as a "freak" issue, despite its occurrence in two consecutive qualifying sessions.
The MGU-H recovers energy from the turbo and controls its speed to ensure optimum boost pressure, making it a fundamental component in the operation of the power unit. For the second weekend in a row, Hamilton's qualifying was cut short due to a problem with the MGU-H on his car that manifested in a lack of power on an outlap.
The failure, originally believed to be down to the insulation of the MGU-H, has occurred on both power units used by Hamilton this year and has not been replicated on either Nico Rosberg's car or any of the Mercedes engine customer cars.
"I would say that what happened today is a bit of a freak failure because it is a scientific assessment process and we had a failure in Shanghai that we understood," Wolff said. "We decided to change the parts and here we go again, the same thing happens so we need to find out if we have identified the root cause of the problem. The car is rock solid, it is a fast car, this weekend probably the fastest so far as we have had these two unfortunate problems on the MGU-H.
"I think we have eight power units out there [in all the Mercedes-powered cars on the grid] and seven didn't have any problems and one had a problem twice. You need to turn every stone and looking at settings, because it happens in the same circumstances in qualifying twice or in the race, so I wouldn't exclude anything but it is not something that is obvious because we would have found out." Asked if the problem could be linked to something Hamilton is doing in the cockpit, Wolff said: "It is certainly not Lewis. We need to look at settings maybe, on the MGU-H."
And Wolff also ruled out speculation that the problem could be linked to a pre-season decision to mix up the mechanics on the cars of Hamilton and Rosberg.
"The crews are doing a great job. We changed the chief mechanic and some mechanics on the car, it is an unfortunate run. Nothing to do with that."
Mercedes has not yet decided which, if any, components it will change for Sunday's race.
"There are many [people] working at the moment to find the root cause and what we can do. Whether we need bits from Brixworth that need to been flown in or not, and then what parts we exchange or not. I can't say what we are going to do because I don't know."