The Dutchman was running second behind eventual Australian GP winner Charles Leclerc when he was forced to park his RB18 shortly after starting his 39th lap.
After the race Horner insisted that there was no connection to the problem that affected both Verstappen and teammate Sergio Perez in Bahrain, where the issue was in the fuel tank.
The Australian failure was external to the tank, and as such came under the responsibility of Honda rather than the team. The broken parts were quarantined after the race, and returned to the Japanese company’s base in Sakura.
“We've been working with our colleagues at HRC in Japan, and they found the issue and they resolved it,” Horner told Sky F1.
“And I believe we have a fix for this weekend. It was just very, very unfortunate, a part that's done tens of thousands of kilometres without ever an issue unfortunately appeared at exactly the wrong time in Australia.”
Asked by Motorsport.com if the issue was related to porpoising and the associated vibration he said: “No, I don’t think so. Further investigation has shown it was something else. Just an issue with a fuel line component. The HRC guys have looked at it very closely and have a fix.”
Horner stressed that after three retirements in six starts the team is determined to score well in Imola.
“It's an important weekend for us,” he said. “I mean, there's a lot points available this weekend, and we want to make sure that we're there to capitalise. We can't afford the gap to grow again to Ferrari, so we need to start eroding it rather than seeing it grow.”
Perez said he was encouraged by the fact that between them the team and Honda had been able to understand and address the early problems.
“First of all, what gives us hope is that all the issues, all the reliability problems that we’ve had, we understood them, and we were able to fix them,” said the Mexican.
“So from now on, hopefully there are no more surprises. Something unexpected can happen still, but we feel like we’ve got on top of them.
“That will be critical for us on our side as a team to make sure we are able to collect the points we are able to get weekend by weekend, because so far, it’s been extremely painful.”
