Blinking temperature light is on 2002 Jetta

A blinking light means blocked exhaust system get it check ASAP

do you know what codes you have,

Yes they are right this needs a dealer and special diagnostic equipment.

it may just mean the oil needs topping or you need a filter change

that happens sometimes dont worry. As long as the light isnt blinking it is fine. Just drive it for a few days. If it doesnt clear itself, take it to a shop and have then clear it for free or cheap. You could also disconnect your battery for 15 minutes or so and it will reset the computer and whipe the check engine light off. Sometimes if you have a bad plug or all cyclinders arent firing it causes the check engine light to come on. now that everything is replaced just do what I said above.

You've lost engine coolant somewhere, and need to fill the engine back up with the VW special G12 coolant.

Then find the leak, which will be in one or more of the following places -
Water hoses to heater core, including any other coolant carrying hoses in the engine compartment
Radiator hoses
Plastic manifold bolted to side of engine which is known to leak (have replaced on an '01 VW Beetle, and an '02 Jetta, both members of our family in the past few years.).
Overflow reservoir cracked
Radiator leak.

Reply back what you find. If the engine got too hot, you may need to have the thermostat replaced.

i had the same problem, it should be the speed sensor on your transmisson after a while your speedometer will stop working. no clue on the lamp...

is the car running. You are probably just waiting for the glow plugs to warm up.

dealer only

It should tell you in your owner's manual.