Hi all had the above vehicle in for service,the guy said on occasion his glow plug warning light comes on and the vehicle looses power.Didn't get any codes think it might have been somewhere else and they cleared them thinking it might solve the problem.The light is on now but the vehicle is running fine.Fuel filter changed on service and EGR valve looks good too.Any help on this would be great as I'm a bit in the dark on it.

Thanks in advance
Dominic