Pierre Gasly will once again start from the back of the grid at the Mexican Grand Prix after Honda concerns over the power unit he used in Austin.

Honda introduced an upgraded power unit at the Russian Grand Prix and first raced it in Japan, and it showed an encouraging step forward in terms of performance. However, a reliability concern meant a further modification was made before last week’s race in the United States, resulting in grid penalties for both Gasly and teammate Brendon Hartley.

While Hartley climbed into the points in Austin, both drivers will use the previous specification of power unit this weekend due to the altitude in Mexico City.

“Pierre is starting FP1 with a new latest spec PU,” a Honda spokesperson told RACER. “The reason for this is that we have a concern regarding the assembly of the one used in Austin. That PU has been sent to Sakura for a full inspection and, at the moment, we are not sure if we can use it again this year. Therefore, by fitting a new one here, we add one to the pool of available units for the rest of this season.

“However, as from FP2 and for the rest of the weekend, Pierre will run an older specification PU. Brendon is also using this spec, for the entire weekend. The reason for reverting to the earlier pre-Russia spec is that we have a better understanding of this version of the PU and are more confident in our ability to set it up correctly for the specific conditions here in Mexico City.”

A new ICE, turbocharger and MGU-H adds up to a 15-place grid penalty for Gasly on Sunday, meaning the highest he could theoretically start is 16th were he to qualify on pole position.

Gasly completed just two laps in FP1 before Honda started changing the power unit for the specification to be used for the rest of the weekend. Hartley will not have a penalty, and is running the latest aerodynamic upgrade in Mexico that Gasly raced in Austin.