It could be although if its a common rail engine they usually start quite well without the glow plugs. You can check the circuit by connecting a meter between the glowplug feed and earth, it should read about 10-11 volts for the duration of the plug function i.e. about 10-15 seconds after you turn the switch to the glowplug position. No reading - the circuit is at fault, anything like 12 volts and one or more glow plugs need replacing.

Possibly coolant temp sensor is faulty & telling the ECU the engine is warm when actually it's cold, so giving a very short glow period.

Oh woe is me :( Seems the glow control regulator is working fine. I took it off, cleaned up the contacts and replaced.

I managed to get the connector off the left hand most glow plug (when looking from the front) and measured the voltage. A pretty solid 12v (no voltage drop from the other 3 connected, which surprised me a little). This voltage was applied for a good 5 seconds EVEN THOUGH the glow plug dash indicator lights still goes out after 1/5 second. (As an aside, I did this 3 times, so 3 x 5 seconds voltage applied to the plugs, and it still needed to crank far too long before starting).

So, I measured the resistance of the plug I could get to. 42 ohms ! I then managed to get the connector off the adjacent plug and that measured 45K ohms ! I assume there must be a current sensing device that is used to light the glow plug dash light (and also indicate to the ECU that all is working well).

So, after 160k miles, it seems I may have to replace the glow plugs, what does the forum think ? The main issue is that the turbo charge inlet pipe runs right across and needs to be removed and even then, access is not that good. Additionally I really don't want to snap any of them off. Any suggestions.

Any idea what size deep walled socket I need ?