The FIA has told Formula 1 drivers to keep signalling with their arms if they stall on the grid, following a confusing situation with Carlos Sainz at the start of the Malaysian Grand Prix.

In Sepang the Spaniard’s engine died as the grid was forming up; his initial reaction was to wave, causing a marshal observing his grid spot to switch on the yellow light.

However, Sainz then pulled his hands back into the cockpit as he urgently tried to restart the car, leading to the marshal switching the light off.

Race starter Charlie Whiting thus assumed there was no longer an issue, and started the race on schedule. However, Sainz only just got his power unit restarted as the red lights went on.

Had he not done so, the risk of a startline shunt would have been high.

This scenario has only become possible with the current hybrid cars. In the past drivers had no chance of starting a dead engine from the cockpit, but Ferrari and Renault drivers are now able to use the MGU-K to restart.

The Mercedes system does not have the ability to start the engine, the team having opted against it for packaging benefits.

At Friday’s drivers briefing in Japan Whiting told drivers that if they stall, they have to keep waving. Sainz pointed out that he needed two hands to restart the car, so in effect from now on drivers will not be able to use the MGU-K, unless their teams develop a procedure that requires one hand.

The other intriguing issue in the Sainz situation is that in theory Toro Rosso broke the rules by giving Sainz radio instructions on how to restart, when no radio traffic is allowed between the start of the formation lap and the race start.

On this occasion the FIA let the issue go – given that there was a safety implication had Sainz not been able to start – but it has now been made clear to teams that similar messages will not be allowed.

Gallery: FIA reminds F1 stars to wave frantically if they stall