Verification conditions
The battery voltage must be at least 11.5 V.
The fuses in the glow plug supply circuit must be in good condition.
The engine control device must be in normal condition.
Examination
Turn off the ignition.
Disconnect the electrical connectors from the glow plugs.
Connect the LED test lead to the positive (+) terminal of the battery and connect the other terminal of the LED test lead to the glow plugs one by one (see fig. 4C.6). If the LED lights up, the glow plug being tested is OK. If the LED does not light up, the glow plug being tested is faulty and must be replaced.
Removal
Unscrew the electrical wires from the glow plugs.
Remove the glow plugs using the HAZET-2530 or VW-3220 key.
Installation
Screw in the glow plug and tighten it to a torque of 15 Nm.
Do not exceed the tightening torque of the glow plug, otherwise the annular gap between the working and threaded part of the glow plug will be reduced or completely closed.
Connect the electrical wires to the glow plugs.
(The original article is available on the website: AudiManual)