What we know about worrying new Honda F1 reliability issue

Honda's worrying return of reliability problems includes a new issue, the root cause of which it might not trace before the end of the Formula 1 season.

Aston Martin and engine partner Honda suffered their third DNF of the triple-header in Brazil, when Lance Stroll retired for the second race in a row.

Stroll had two separate battery problems over the course of the Brazil weekend and didn't make it to mid-distance in Sunday's grand prix.

It means Stroll has finished just six of the 20 races held this season, while team-mate Fernando Alonso has had seven retirements of his own.

There have been some flashes of optimism - in relative terms, given how disastrous this first season of the new alliance has been - of late as Alonso scored points in Malaysia five races ago, had surprisingly good pace at Austin despite sustaining significant floor damage on the opening lap, and excelled in the wet in Brazil.

There, Alonso comfortably gave Aston Martin and Honda their best qualifying of the year, getting into Q3 for the first time and lining up eighth on the grid.

But this has been badly undercut by a return of significant fragility that's closer to how badly Honda started 2026.

Reliability problems also put paid to Alonso's chances in Mexico, where he had looked quite competitive and closer to the top 10 than normal. The issue was related to the cooling system inside the energy recovery system, whereas in Brazil the emergence of battery problems for Stroll sounded a clear alarm bell.

Shintaro Orihara, Honda's lead trackside engineer, acknowledged that "we know what happened, but we don't know what is the root cause".

He admitted it may take a few weeks to find that, but already from the data there needs to be some kind of countermeasure for the next race in Las Vegas, while Honda traces the underlying cause so it can be addressed properly for 2027.

"We need to find the actual root cause of this error for next year," he said.

"Otherwise, we keep having the same issue."

This was a different kind of failure to what had occurred in Mexico, which had led to MGU-K problems. But the theme is similar: in Mexico, Orihara had admitted to a lack of robustness within Honda's engine in more ways than one, and the fault there hadn't shown up in simulation.

Now Honda knows what happened but doesn't know why. That's a worrying through-line between the two issues. It also harks back to the start of the year, when Honda could identify the obvious catastrophic consequences of the problems that were emerging and could see broadly where they came from, but didn't know exactly what the problem's root was, because it had come out of the blue compared with what it had experienced on the dyno.

What's particularly alarming is that this does seem to be a regression from where Honda had got to in the middle of the season.

Its performance was obviously still lacking, and its engine is still underpowered on the internal combustion side, even with upgrades through the year to try to trim the deficit.

But it had at least got to a point where its cars were finishing races, which allowed Alonso to score some points when the Aston Martin was heavily upgraded.

Either side of the summer break, Alonso had five straight finishes, and Stroll got two of his six finishes this year in three races before the summer break too.

Orihara acknowledged that reliability was simply better in the middle of the season, but that has been replaced by "several issues" in recent races.

Some of this trend could be related to the mileage of parts - components simply coming to the end of their life cycle - or to just a case of Honda trying to run the engine harder for performance and going over the edge.

But with the battery issue that emerged in Brazil specifically, it's too early to say what the trigger was.

Honda has not made the progress it would have hoped for this season in terms of the all-round performance of the engine, and at best has only achieved some of its performance targets in very specific circumstances.

So the fact that reliability has got worse, without a clear upside, puts Honda under pressure and brings an unfortunate amount of negative scrutiny again, right at the end of a year in which it has had to come through quite a lot of adversity.

It is also a curveball for the development work Honda is doing on 2027, when it needs to take a step in both performance and reliability.

Everything that has been indicated so far is that there will not be a major step at the start of the new season. There's already a plan to phase in further upgrades through the year. But that work will already be deeply under way.

Troubleshooting takes away human resource, limited dyno hours which are restricted under F1's engine development limits, money that comes under the engine cost cap, and simply time because the clock is ticking to the start of 2027.

First the cooling issue in Mexico, whatever that was exactly, and now this on the battery side, takes Honda's focus away from a path that it would ideally be a lot further down.

Honda CEO Toshihiro Mibe was in Brazil, which Orihara said has a galvanising effect on the staff - "but on the other hand, we had a battery issue twice this weekend".

It was not exactly how Honda's F1 operation would have liked to present itself in front of the big boss. But, as Orihara noted, Mibe at least "knows what is happening trackside".

"He will bring this experience to the Japanese side and also boost our development," said Orihara.

If there was ever any possibility of complacency creeping in about how much work Honda has to do to reach the necessary standard, the CEO seeing first-hand the kind of problems still being encountered this deep into 2026 will have stamped it out.