[Vwdiesel] how do I know I have a bad glow plug in newer TDI

[James Hansen]

> that if something else goes wrong you won't know because the light is
> already on and you'll never notice a difference, happily assuming it is
> only on because of the plugs.  

Never fear because if something really goes wrong, the MIL lamp flashes to
indicate an immediate shutdown is necessary.  Steady light means there is a
problem that is not fatal, and is safe to keep driving.

DO NOT test any glow plug newer than a 1Z motor with 12v.  They use less
voltage and will burn out rather spectacularly.  Ask me how I know this....
They quickly get really white hot and look like a kid's sparkler, right
about the time your "Oh crap" alarm goes off, the festivities end. So if you
want to take pictures, be ready, it's quick.
Test them for simple continuity to ground. A test light clipped to bat + for
instance, and ground the pointy end through the glow plug.  I have never
seen one fail to ground, although then your gp fuse would be blown, and
master diagnosticians we all are would have checked that first anyway... :-)
-james