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Check engine lite produced a glow plug system DTC. Glow plugs check satisfactory; glow plug relay (104) checks satisfactory. Glow plug fuse (50amp) checks okay. Battery voltage at pin 30 on relay checks to 12 volts. Glow plug lite comes on momentarily with key to run, as normal, but no actuation of relay to put voltage to glow plugs. Door open switch, actuated on and off seems normal. Can't find much information on the automatic glow time control module (supposed to be behind the instrument panel) or even if this car (1997 vw jetta diesel) has one; VW Parts had no clue about where or what it is. Obviously, there must be some method to time glow plug actuation below a fixed ambient temperature. Don't want to jump into dash without "more input" information. Any help is appreciated.
 

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Is your car having problems starting or has it just thrown a code? If it's just thrown you a code I read somewhere that the most likely problem will be the glowplug wiring harness and that you should clean each plug connection with a bit of fine sand paper or replace the harness. I've no idea where the module is sorry.
 

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The door switch is a red herring. That may have been on earlier cars but it has nothing to do on any TDI despite it being mentioned in official literature. What is the glow plug code?

Maybe the coolant temperature sensor thinks the engine is warm so there's no need to use the glow plugs? This can be quickly verified if VCDS sees anything other than ambient temps on a "cold" engine.

The GP normally don't light below 48 degrees F before engine start. They do light after every engine start (below 2500 rpm) regardless of temp.
 
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