2007 vivaro m9r?

Follow the glow plug wire back to the relay and check that.
But be warned,
more than half of these I see have shorts in the wiring harness.
Which can throw up all kinds of faults.
That fault description sounds a little OBD generic,
Better quality diagnostic tools will give better results,
like short to earth,short to +,open.............
Get it rescanned.
The plugs on these are only supposed to come on at VERY low temperature,

1/4drive
May 2014

Very difficult to say but have you actually measured the voltage available at the actual glow plugs themselves? I am not sure on your model but a lot of modern motors glow plugs are operated at 4/5 volts which is why some people burn them out testing them with a 12v battery and should be tested by measuring resistance with a meter,if the readings don't tally with what they should then a good wiring diagram would be useful to determine what control units and relays are in the system and where they are located and also what voltages are required for operating the glow plugs themselves,good luck

cdc
May 2014