About a week ago my car went nuts. Here’s a pretty accurate description from another Passat owner with similar woes:
…the electical [sic] system just goes crazy when its on. Problems consist of random warning lights coming on like oil, gas, etc. Windows randomly not working. Engine running ruff. Transmission only working in 4th gear, with all gears indicated as being selected on the gauge cluster. Tach bouncing wildly all over the place not in sync with the engine at all. Then other times it decides not to screw up (usually for only like 5 mins tops) and nothing is wrong at all with it and it’s like the great car I used to know. [link]
This happened once before, long ago, but the problem vanished and I attributed it to some sort of soft error in the car’s computer. This time the problem persisted and worsened, so I had the car towed over to Sam’s shop, MotorConcepts, in Concord.
Sam is a good man, in my experience; he worked on my car before (catalytic converter issue, a year ago). He told me I needed a new battery and alternator ($800-900), but called back soon after and told me he found some wiring issues and that the alternator might not be bad after all.
In the end, the problem was exactly what the owner of the above quotation had been advised to check: cable and grounding. A corroded or just plain old connection had finally given way. Specifically, the cable that connects the ECU to the alternator / harness. [My terminology here is confused; help appreciated.]
In the end it cost $300 to fix the connector, including a new Interstate battery and corresponding labor. The connector is now soldered on solidly and shouldn’t cause any further problems.