2003 Jetta Coolant temp sensor diag
 

Hey all. New here, and trying to help out a friend.
I am a DSM freak, so VW is a little different for me, but the basics should be the same.
My friends car started over heating for no apparent reason last night.
I looked over her car, and checked the normal things (coolant lvl, belts, water in oil, oil in coolant, no smoke indicating a blown head gasket, etc) but could find nothing wrong. No, I am not an expert, but basics are basics. The CEL light is also on. She had the thermostat replaced back in August, and has had no problems until now.
Last night when it over heated, she added coolant, and it still had the overheating problem.
I am wondering if the coolant temp sensor is faulty. I would like to test it, but can find no instructions on how to do that with a DVOM (Digital VOlt Ohm Meter).
Can anybody give me a hand on this? I don't want to engage in "shotgun" mechanics, and even then, maybe end up being wrong.
Thanks in advance.

***EDIT***
Something else I was thinking of would be a blockage in the radiator, or a problem with the water pump. I have tried to identify the engine code, but as I do not know VW's, I am not sure how to ID the engine code.
Oh yeah. It is a 2.0 N/T.

My 2003 Jetta GLS 2.0L is not overheating, but I have some cooling system issues too. Flush the coolant system first before going any further, and be sure to use only the pink VW coolant from the dealer (VERY IMPORTANT)!! Also, try back-flushing the radiator too. If the flushing doesn't help, the water pump might be bad. If this is the case, I would think that the car's heating system might not be working properly (due to lack of circulating coolant throughout the engine and heater core). If it is the water pump, it's not going to be cheap. What's funny to me is that the pump, if I'm not mistaken, is powered by the timing belt, so check the water pump next. It is possible too that the newly installed thermostat has gone bad as well. Unlikely, but possible I suppose. I doubt you have a sensor problem. Good Luck!