Spanish Grand Prix: Honda software problem forced Alonso out

The Spaniard qualified 10th as McLaren made Q3 for the first time since rejoining Honda for the 2015 season and was running 12th when he pulled over to the side of the track reporting a loss of power.

"I'm not sure the exact cause but a software command issue happened and it stopped the engine," Honda chief Yusuke Hasegawa told Autosport.

"The engine itself is fine, we can even use it for Monaco.

"It stopped on the circuit so we need to check if that created any damage because of the high temperatures."

Alonso said the team was managing the problem before the engine cut out.

"A couple of laps before we stopped there were some sensors failing and I had some message from the team on the pit wall and we were managing the problem somehow but in the end it wasn't foreseeable anymore," he said.

"I'm very sad. Obviously it was a big opportunity, especially with the Mercs out of the race.

"We're not happy with the reliability yet.

"We need to keep improving and also we need to look at how the racing went.

"I could not show my pace at any point in the race.

"We didn't have a good start and after that I just followed Jenson so we need to keep improving."

Despite the retirement Hasegawa, who added this particular software problem had not happened before, believes Honda is making strides with its reliability.

"This is the fourth race for Fernando's engine," he said. "We never survived that long [before].

"We didn't finish but it was a system failure. We were about to prove our engine can last four events, which is very encouraging for us."