Glow plug light goes out quickly on every start

[Denver_Diesel]

2000 Jetta TDI manual

Here's an interesting situation. I've searched the forums and can't find a similar instance. I recently had my timing belt replaced by Andersen Automotive in Golden, CO - along with the tires, engine oil and other fluids (it was a heavy maintenance cycle - i wasn't motivated enough to do it myself).

Anyway, before taking it in I got to know the car quite well, obviously. Upon starting the ignition sequence the behavior of the glow plugs as indicated by the dashboard light in the instrument cluster was this: The glow plugs would stay on for a length of time inversely proportional to the outside air temperature. That is, the colder it is outside (assuming the car has not been running in the last several hours), the longer the glow plugs stayed on. This makes perfect sense, and the best I could tell the relationship was linear. A rough approximation is that if it was freezing (0 deg. C) the plugs would stay lit for inbetween 3 and 4 seconds. If it was pretty hot outside (say 40 deg C) then the lights would stay on for less than a second. You get the idea. Ok, now for the interesting thing. Since the TB was changed, the glow plug lights have no temperature dependence. Regardless of the temp. of the engine block, they stay on for less than a second every time. Any insight for me??

thanks

 

[Long_Range]

I'm not trying to make a diagnosis. You might try reading threads Related to the coolant temperature sensor. Here's a thread to start. Hope you find something useful.
thread

 

[weedeater]

Two things, considering your altitude: the time is dependent on both the temperature (lower=longer) and altitude (higher=longer).

An open circuit for the temperature sensor equals lowest temperature.

In your case it would imply a short. You would need a vagcom or similar to see what the computer is seeing for the temperature at startup. Same for air pressure (MAP) at startup.

 

[tadc]

I'd suspect the MAP. At high altitude(assuming all of these events occured in denver), the GP light should stay on for several seconds even when the outside temp is relatively warm. Perhaps the mechanic failed to reconnect the MAP sensor (on top of the intercooler)? Actually, from your description, it sounds like the GPs weren't functioning correctly *before* the work was done.