All Glow Plugs are Not Equal
Be aware that there are two suppliers for the Volkswagen TDI diesel glow plugs (Bosch and Beru).
An example is the TDI-equipped 2011 VW Tourareg.
When replacing glow plugs, it’s important not to mix brands. The vehicle must have the same brand glow plugs, or DTC P-380 (glow plug monitoring) may set.