  The Exceptional Supersymmetric Standard Model (E$_6$SSM) is a low energy
alternative to the MSSM with an extra $U(1)$ gauge symmetry and three
generations of matter filling complete 27-plet representations of $E_6$. This
provides both new D and F term contributions that raise the Higgs mass at tree
level, and a compelling solution to the $\mu$-problem of the MSSM by forbidding
such a term with the extra $U(1)$ symmetry. Instead, an effective $\mu$-term is
generated from the VEV of an SM singlet which breaks the extra $U(1)$ symmetry
at low energies, giving rise to a massive $Z^\prime$. We explore the
phenomenology of the constrained version of this model (cE$_6$SSM) in
substantially more detail than has been carried out previously, performing a
ten dimensional scan that reveals a large volume of viable parameter space. We
classify the different mechanisms for generating the measured relic density of
dark matter found in the scan, including the identification of a new mechanism
involving mixed bino/inert-Higgsino dark matter. We show which mechanisms can
evade the latest direct detection limits from the LUX 2016 experiment. Finally
we present benchmarks consistent with all the experimental constraints and
which could be discovered with the XENON1T experiment.
