Where exactly is the 409 relay?

SOURCE: 2000 Volkswagen Jetta TDI WITH NO POWER

find your local vw service center and see if they can plug their computer in to see if there are any codes on the cpu. there may be one for an intermitent for the turbo. i ran into the same problem last month and it was the turbo veins are sticky so occasionaly it lack power going up hills. it did not cause the check engine light to come on, but there was a code on the cpu when they checked it. if it happens again while you are driving, pull over, shut the car off for 10-30 secs then restart it and see if it makes a difference. when it happened to me i called my guy and thats what he had me do and it was like a new car after that.

SOURCE: turbo control/control limit below minmal level jetta 2000 tdi

This happens to almost every TDI. On top of the valve cover there's a puck-shaped device with a 90 degree plastic tube connected to the intake. This is your crankcase vent... and your culprit. I fixed mine using heater hose. For detailed instructions visit TDIclub.com- a must for every TDI owner

SOURCE: 2000 Jetta 1.9 TDI is reading 2 codes for electrical connecton

The torque converter clutch circuit is built onto the tranny. You can see the plugin. You can disconnect this and will be ok, Otherwise it is expensive to fix

The crank sensor sends informaiton to car's computer telling it to give power to the motor. If the crank sensor is shot, then your car probably will turn over but won't start. Or won't always start until it is completely bad and won't start at all.

You can go to autozone.com and register for free, then you will have a full free online repair manual

SOURCE: jetta 2000 tdi 1.9 i need location tr switch code

The switch just may be out of adjustment.

its location is on the transmissiom by the shift cable bracket

SOURCE: 2000 Jetta TDI: How do I change spark plugs on 2000 VW jetta 2.0...

You're in the TDI (diesel) solutions section so it uses glow plugs.
If it's a petrol engine 2.0L then it would be accessible above and below intake manifold using a swivel spark plug deep socket.