mercedes E320 CDI 2002 W211 Glow plug problem

hi, have problem with no voltage at glow plug leads, Feed to glow plug module from ecm pin 43 is reading between 6 to 8 volts, is this sufficient to operate the relay in the glow plug module? Feed to glow plug module is 12.5 v and earth is ok. Any other suggestions would be appreciated. Regards.