P0036 or 16420 on your Volkswagen Jetta

P0036 is flagged by the computer when it sees a problem with the downstream oxygen sensor circuit. As far as you are concerned, you should change your oxygen sensor and see what happens. There is a 95% chance that this will fix your problem.

Here is the link for the correct oxygen sensor to buy: Bosch 15160

The other but not likely posibilities are the ECM or a wire in between.