2004 PASSAT GSL STOP CHECK COOLANT LIGHT CAME ON

SOURCE: 2004 Volkswagen passat transmission code p811

as per vw, you need to check transmission oil level., not an easy thing to do. if transmission oil level ok (no dipstick on these by the way). it is a mecahnical fault.

SOURCE: Check Coolant / STOP lights

If the coolant level is low in the expansion bottle then the light will come on and you need to locate the leak. If the bottle is full then the level sensor in the bottle is bad!

SOURCE: VW passat coolant warning light on

There's a level sensor plugged into the bottom of the coolant reservoir. Unplug it and clean the contacts with electrical contact cleaner. If that doesn't do the trick, replace the sensor.

SOURCE: My 2002 vw passat check

There is a coolant reservoir on the driver side of the engine compartment. You just need to take the cap off and add coolant to the max lever when the car is cold. Never open it with the engine hot. Then you need to use the coolant type G12. You won't find it anywhere else but directly from the dealer. Its very important to use the this type of coolant so you dont damage any component of your cooling system. You're be paying about $17.50 per galon of G12 or price may be different depending of which state you're at.
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SOURCE: I have a 2004 vw

1. Your problem is cylinder head gasket out of order! You need to replace it. Stop the car and replace the cylinder head gasket. Check out also the cylinder head flatness when removing. Rectify if necessary the cylinder head contact surface at a specialized workshop. Fit a new cylinder head gasket with new bolts!
2. You have only oil leaking into the cooling system (coolant reservoir) because the oil pressure is higher than coolant pressure! It's normal this happened.
3. I will send you back the cylinder head replacement instructions with tightening order picture, and tightening torques for each step.