VW Golf IV TDI glow plug operation?

Typical diesel starting is: 1) ignition on, 2) glow plug indicator comes on, 3) wait several seconds for indicator to turn off, 4) crank the engine to start. On my car, 1-3 happens; but, there is no power to the glow plugs. Funny though, when I am cranking, the glow plug circuit comes to life and it remains... show more Typical diesel starting is: 1) ignition on, 2) glow plug indicator comes on, 3) wait several seconds for indicator to turn off, 4) crank the engine to start. On my car, 1-3 happens; but, there is no power to the glow plugs. Funny though, when I am cranking, the glow plug circuit comes to life and it remains powered for roughly 45 seconds even if the engine starts. Many times on diesels, the glow plug remains on for a period of time to make sure the cylinder reaches sustaining heat. Is there a second circuit to power my glow plugs before I start cranking? I resorted to a manual house switch to preheat since my car was not working cold and it fired right up. Maybe there are two circuits that activate the glow plug. These new fangled computer cars have taken a relatively easily maintained device and made it practically impossible. I've gone to the VW dealer mechanics and found them unable to answer simple questions like this while being very good at taking a $20 job and charging $1,000. Anyone have a better grasp of my car's glow plug operation?
Update: Update: This is summer with ambient temperatures of 50-70F. My internet searching has indicated the glow plug programming uses the coolant temperature anor inlet temperature in its decision process. I did find some air getting into the fuel line via a new/faulty fuel filter now replaced. On cold startup, the... show more Update: This is summer with ambient temperatures of 50-70F. My internet searching has indicated the glow plug programming uses the coolant temperature anor inlet temperature in its decision process. I did find some air getting into the fuel line via a new/faulty fuel filter now replaced. On cold startup, the glow plug comes on during cranking and stayed on for 3 minutes. When the coolant temperature was warmed to 120F, the glow plugs stayed powered for 40 seconds. They did not come on nor stay on once the engine/coolant was at operating temperature. These glow plugs get red hot in a few seconds. I have no confirmation regarding any glow plug operation prior to cranking! Maybe its too warm, maybe it never preheats, and maybe a second something IS malfunctioning. There are also three glow plugs in the air intake of which the operation I know nothing at this point. The supersecret computer program and tight-lipped (or incompetent) local stealership makes all this a sort of blac
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