Johan Bijnens, Ilaria Jemos Determination of Low Energy Constants and testing Chiral Perturbation Theory at order $p^6$ (NNLO) Abstract We present the results of a search for relations between observables that are independent of the Chiral Perturbation Theory (ChPT) Next-to-Next-to-Leading Order (NNLO) Low-Energy Constants (LECs). We have found some relations between observables in $\pi\pi$, $\pi K$ scattering and $K_{l4}$ decay which have been evaluated numerically using fit 10 in \cite{Amoros:2001cp} for the NLO LECs. We also show some preliminary results for a new global fit of the NLO LECs LU TP 09-24