Technical Description of OBD-II Trouble Code
“A” Glow Plug/Heater Circuit
What does that signify?
This code is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may vary slightly depending on the model.
The description for GM vehicles is slightly different: Glow Plug Performance Conditions.
The glow plug operates when starting a cold diesel engine (the powertrain control module PCM uses the coolant temperature when the ignition is switched on to determine this). The glow plug heats up red hot for a short period of time to increase the cylinder temperature, allowing the diesel fuel to ignite more easily. If there is an open in the glow plug or circuit, this DTC will be set.
On some diesel engines, the PCM will operate the glow plugs for a period of time after the engine is running to reduce white smoke and engine noises.
A typical diesel engine glow plug:

Basically, the P0380 code indicates that the PCM has detected a fault in the glow plug/heater circuit “A”.
Note: This DTC is very similar to P0382, which refers to circuit “B”. If you have multiple DTC codes, fix them in the order they appear.
Performing a quick Internet search shows that the P0380 DTC seems to be more common on Volkswagen, GMC, Chevrolet, and Ford diesel-equipped vehicles, but it is possible on any diesel vehicle (Saab, Citroen, etc.)
Symptoms
Symptoms of a P0380 trouble code may include:
Potential Causes
Potential causes for this DTC may include:
Diagnostic Steps & Possible Solutions
Other Glow Plug related DTCs: P0381, P0382, P0383, P0384, P0670, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P0679, P0680, P0681, P0682, P0683, P0684.