glowplug

Hi all, So recently I bought a 2014 Astra J ecoflex 1.6 and after 1 day of ownership it's developed a fault. Symptoms - car went into limp mode when I accelerated above 2000 revs. MIL is now illuminated and the code P0299 is showing on my diagnostics and the middle display says "Service...

Can anyone talk me through testing the glowplug relay please? my asssumption is that currently its on its way out but wanted to check for myself while im doing afew other jobs. I have multimeter, opcom etc. Thanks