check engine light no code on 1999 Volkswagen Beetle

how do i figure out what is wrong with the car when the check engine light is on and there is no code.
took it to auto zone everything came up ok

2 answers
Generally if the "Check Engine Light" has come on there will be a code stored in the vehicle's computer and it will be stored until erased using a scantool or the car has completed a sufficient number of drive cycles without having seen the problem reoccur. In this case it has done a self test seen no fault and erases the code.
This being said I have seen cases where one scan tool does not see a code and another brand of scan tool sees a code on the same vehicle. We have three scantools where I work.
I have a 1999 plymouth breeze 2.0 and I replaced the ignition coil, changed the spark plugs. Vishually inspected the wires which were fine. When I replaced everything that could cause a misfire, it still came up codes p300 to p304. I found I had to erase the codes one by one. When I accomplished that, the engine light is still on without any link. I have one of the best OBD11 scanners there is and it wold pick up a minor fluxuation in the circuits. My guess is its the ECM or the onboard computer itself. Have it tested at AZ or a garage. If that doesn't sound right, does anyone have any ideas? I'm going through the same thing as you