This season, the German automaker is seeking an eigth consecutive F1 championship, having been unbeaten during the turbo hybrid era.
But its engine chief, Hywel Thomas, has announced that it faces some early year obstacles as it gears up work for the launch of the 2021 campaign.
In a video released by Mercedes, he said, "We have got some issues with the power units, We know we have issues but we have plenty of plans in place to fix all of those issues. I'm sure it will all be ready for the first race."
In the pre-season build-up, Mercedes is no stranger to facing dramas, and 12 months ago its then engine chief Andy Cowell admitted that the team faced difficulties in its preparations for the new campaign.
Although the team encountered some reliability dramas in testing, by the time the delayed season began in July, it was finally able to get on top of the matter.
Mercedes is currently developing its 2021 engines and has shipped out its customer teams with the first batch of power units.
And although it now runs through reliability testing, new limitations have added to its difficulties that limit dyno use.
In addition, engine homologation rules that rule out modifications to in-season power units mean that everything has to be sorted by the opening race of the season in Bahrain.
Engine chief adds, "This year there have been a few extra additional things thrown at us. It's been the first winter where we've had to react to a change to the regulations, which limits the amount of dyno hours we're able to run. This means we have to make every single dyno run count and must make sure that we are entirely productive, to learn about the performance and the reliability of the Power Unit during each hour"
To continue, "Also, it's the first winter where we have prepared for only one single upgrade for the whole season. So, we have to get all of our performance into the first PU that goes to the first race, whereas in previous seasons we have been able to split that up into different packages for each PU that gets introduced."
To end off, "So, with that challenge, we have to get absolutely everything there for the first race and make sure it's completely reliable."