Scotland

Audi Allroad 2.5 TDI 2004.
Initially the battery charge warning light would go on, volts would sit at 12V, light may go out after driving after a while and volts go to 14V. This went on for two months. Took it to garage, nothing obvious to them. When out one day the car would not start having been driven for an hour before hand, no volts on dashboard and no lights. After a tow start it started but was a reluctant start. Put car on charger and it was fine but the problems returned two weeks later when the battery warning lights came on and again dash reading would go between 12 and 14V intermittently. One morning the car would not start, the lights would work but no volts on the guage on the dash and the fuel guage did not register. The car would give a quick turn over and start for one second then die. The radio went to requiring a PIN. It would not tug start and it was towed to garage the to the garage. The garage checked it over, nothing obvious, took the ECU wiring unit out and put it in again and the car started. Once car came back the battery light came back on and voltage dropped again but would come alright in time. One day after being stopped for approx 3 hours it took a few seconds to start however the voltage reading was dropping rapidly and eventually the central dash battery warning light came on and by time I got home (15 minutes) read no volts and just as I got up the last hill I thought it would stall but instead it got a little extra life and made it to the top. I put a new battery in in case it was a faulty battery cell and when I switch the car on the interior light dimmed to about 20% for 10 seconds then returned to normal. The battery light went out however it did not cure the battery light going off and the switching between for more than 5 minutes. One thing that was odd was on returning from my test run the interior lights started pulsing (when I turned a corner but not always). Do you think this is a voltage regulator/ diode /alternator brushes/ earth fault or water issue somewhere? The car is great otherwise.

georgeb944

Sounds like,an alternator. Have it bench tested, or replace it with a new one.

johnkk

You might get lucky with just a regulator, but with Audi luck, alternator.

Scotland

Thanks, when it was in the garage they said it was all fine, including the short lead - will recheck.

Scotland

Thanks will recheck alternator and voltage control regulator- might be lucky it is a great car.

johnkk

After rereading your original post, I have a hunch that the diodes are blown out. There are usually 6 and when they fail one at a time, the alternator will still function (sort of). Eventually they will all fail and no output from alternator. New alternator time if the diodes go. They can be replaced, but I think easier to get new or rebuilt.