Two problems related to o2 sensor have been reported for the 2003 Volkswagen Jetta. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Volkswagen Jetta based on all problems reported for the 2003 Jetta.
The rear O2 sensor on my 2003 Volkswagen Jetta failed causing the mil indicator to illuminate. The sensor had to be replaced, and is not covered under the extended warranty for emissions.
Ignition coil failed, was told the O2 sensor was bad and needed new spark plugs, I had just replaced the spark plugs 5 days earlier, they only had 11 miles on them, so it cannot be spark plugs, question whether the O2 is truly bad, having ignition coil replaced but was unable to tell whether the catalytic converter is also bad until other problems are corrected.