The check engine light in my Rabbit came on in January of 2011, just after I’d had it inspected. After hitting a dead end with the local VW dealership regarding diagnosing the vehicle (they wanted to charge me $75 to plug it in, but then said if the car was running fine, I could drive on it), I opted to drive on it. At a later date, I had the code read elsewhere and discovered it was the O2 sensor. After doing some research, I discovered the emissions system is covered under an 8-year, 80,000 mile warranty. My car was sitting around 72,000 when I realized this. As such, I chose to have it fixed.
Dealership found a blown O2 sensor and corroded wires. They ordered the part and called me to come in TWO weeks later. They repaired the wire, but had (likely) ordered the wrong sensor, so I had to go back in again. Brought it back in, they replaced the sensor. 2 miles off the lot, the light came back on. Took it back the same day and they found (and fixed) more wire corrosion. About two start cycles later, the light came back on.
At this time I chose to take the car down to another dealership. They spent 6 hours with it, repairing more spots of corroded wire, but still couldn’t get the light to stay off. They theorized that the sensor had been blown so long/so badly/repeatedly that the related sensor for the ECM was now confused. Made plans to bring it back two weeks later to have the ECM replaced. Approximately 4 to 5 start cycles and less than 100 miles later, the light is now back on.
Now, I know that the rear O2 sensor monitors the levels for the catalytic converter. I’d be happy to continue with my light on, except that it shuts that O2 sensor off if it thinks there’s an issue. Eventually this is going to affect my mileage even more than it already has. My thinking is that despite what the codes say, it is now the catalytic converter (something I dread to have to pay for). Are there other theories regarding this?