Doubtful that both key fobs failed simultaneously...

..reread the instructions and try again. Specifically, the key position in the ignition.

Also, make sure you do this with the door closed..on some models it matters...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car