On a day that would start damp in the morning but would recover to be sunny later in the day the WilliamsF1 team would complete their four day test at the Jerez circuit. Conducting the days testing would be Mark Webber and Alex Wurz. Both drivers would continue setup and reliability testing of the new FW28.

The end of the day would see Alex finish eighth fastest but he was to suffer a few mechanical problems with his car that would prevent him from completing long runs. Mark's time out on the track would finish after just fifteen laps when he was to suffer a gearbox problem that would send his car off the track. Mark was not able to continue testing due to a lack of spares for his car. He would finish the day slowest.
 

WilliamsF1 Team Technical Director Sam Michael commented on the days testing.

Michael said: “After a wet morning, the track dried out around lunchtime. Alex continued working on reliability running for the engine and gearbox, while also fitting in some set-up work. Unfortunately Mark had to stop early as we were short on suspension spares with which to repair his car after an off. Overall, Jerez has proved to be a good test for reliability with the FW28, and we now look forward to Valencia next week and working  on further set-up options and carrying out tyre testing with Bridgestone.”

Simon Corbyn, Head of F1 Race Engineering, Cosworth summed up the four days of testing by saying: “Cosworth had a good week in Jerez with WilliamsF1. The latest CA2006 performance developments were successful, plus the engines ran in excess of the two race weekend life requirements with no issues. The Bahrain GP CA2006 Series 2 engine specification, which incorporates further performance and reliability updates, will track test next week in Valencia and the priority for the engine development programme will now shift to delivering the further upgrades scheduled for introduction during the 2006 season.”