I have a 2000 TDI Jetta and I would like to check the glow plugs to see if I have a bad one how do I do this?
Is the MIL (check engine) light on? If not, then the glow plugs are fine. The easiest way to check the glow plugs is with an OBD2 scan tool. There are specific codes for the glow plugs that will tell you which, if any, are bad. You can check them manually with a 12v test light. Connect the test light to the positive (+) battery terminal. Pull the glow plug bridge off and touch the tip of each glow plug with the test light. Light on means it's probably good. Light off means the heating element is broken inside and the plug is bad. Remember... there are two different brands of glow plugs that were installed in the TDI's... Bosch and Beru. You can NOT mix the two brands. All four glow plugs MUST be the same brand or the computer will generate a trouble code and turn on the MIL. You can tell which ones you have by looking at the top terminal... a single ridge or ring is a Beru plug. A double ridge or two rings is a Bosch plug.
I had a Bosch glow plug fail about 10K miles ago. Replaced all four with Champion glow plugs from O'Reilly's for less than the dealer wanted for one Bosch. So far so good. YMMV.
I had a problem recently. Either test light or ohm meter. If it's good light will go on, and ohm meter will show #'s. Bad no light and meter will show 0.00 or OL. No tools? Pull the plug and put a dab of grease or oil on the end. Tun the key, if the plug is good the oil or grease will melt/burn off. Be careful the plugs get hot. And the must be grounded.