Volkswagen Motorsport has confirmed it's found the source of the problem which forced World Rally Championship leader Sebastien Ogier and his team-mate Jari-Matti Latvala into retirement at last month's Rally Argentina.

The German manufacturer said it was going to run a full post-mortem into the double mechanical breakdown and VW is confident it has identified the fault Ogier and Latvala suffered from.

After analysis on the Polo R's engines at its Wolfsburg factory it was revealed both had a fault in a fuel injector, meaning the cylinder connected to it was flooded with too much fuel.

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"It turns out that part of the fuel injector broke whilst the cars were running. The broken fragments blocked the mechanism of the fuel injector, thus preventing it from working properly," Dr Donatus Wichelhaus, Volkswagen's head of engine development said to WRC.com.

The problem forced Ogier to stop after 45km of the opening leg from Agua de Oro to Ascochinga. Latvala retired while running in third position during the first pass through the El Condor test on the final day.

To resolve the fault the German squad will use a different specification of Bosch fuel injector at this month's Rally Portugal. The updated piece is a homologated part and will need VW to use a 'joker' token to apply the improvement.

Rally Portugal is set to run between the 21-24 May and act as round five of the 2015 World Rally Championship.