I have a ‘94 Mercedes C280 with 182k plus miles on it. I have couple of issues. Maybe they’re connected – maybe they’re not:

1 - At the start of the year my speedometer and odometer stopped working. The speedo needle does not move and odometer numbers don’t change. I assumed it was a bad sensor. But how do I know if I need to replace the front or rear sensor? From what I’ve learned thus far about replacing the front sensor, it sounds like that if you can change a tire and twist a wrench, you can replace this sensor yourself.

2 - Some weeks later (for months now) my battery light would come on while driving and on go off, usually while at a red light or when I stopped. Eventually (now) the light just stays on. I tried to check the codes with my trusty code reader and I kept getting error messages. I finally took the car to a couple auto parts stores to have them pull codes and to my surprise, their code readers didn’t work either.

While at the second store I told them about my battery warning light and odometer issues, and they suggested I check the fuses. The fuses were fine.

Then they tested my battery. They said my alternator and diodes are fine but the regulator is bad, and I’m basically driving on battery power because the alternator isn’t holding a charge.

So it sounds like I should replace the entire alternator. I understand this job is something that any competent mechanic can do. (Translation: I do not need to go to the dealer) and that I should stick with a Bosch alternator for replacement.

Replacing the alternator should take care of the battery light, but I’m not sure how that would suddenly make the code reader port functional again. Does any of this sound about right?

Thanks for your responses.

 

How old is your battery? They can out bad in as little as two years.