Replaced alternator, electrical disaster.

Faust · Post by **Faust** » 18 Jul 2016, 18:26

I should begin by saying that I have never met an electron that I liked. In any case, I recently replaced the alternator on my 2004 V70 with a used one from a 2004 S80 T6. It may be important that during the bad alternator period, I had to recharge the battery several times. IO took it for a ride and stopped at a "C" store, up to then everything seemed fine. When I restarted it, my A/c fan was gone, the power window didn't operate, "Brake" and "ABS" lights were on and it ran in limp mode. Shortly I got the "Engine system service required' Message. I put a meter on the battery and am pretty sure I was getting 7 volts. Hooked up charger and let it idle. Quit at idle. Power windows and A/C fan intermittently returned.

I did disconnect negative cable while switching alternator. Battery is fairly new, everything was fine before replacing alternator. Any guesses?

Any point to leaving cable off overnight in hopes of a reset?

Post by **oragex** » 18 Jul 2016, 19:04

like said, if you kept the old alt, swap the regulator

rimutakaman · Post by **rimutakaman** » 18 Jul 2016, 19:12

If you are only getting 7 volts out of your battery, that is way too low and I would suggest, the source of your problems. You did not say if those 7 volts was with the engine running or not running, but in either case, that voltage is way too low. With the engine running you should get I3.5+ volts, and not running, your battery should read around 12.5 volts -- if the battery is fully charged. I would focus on the ground for the battery and the battery itself. If you have a battery charger, I would leave that on overnight and reassess in the morning with a fully charged battery.

Faust · Post by **Faust** » 18 Jul 2016, 20:02

I undid the negative cable and hooked up my charger at max for about an hour. Disconnected charger and started it. Started right up, all messages gone, all dash warning lights off, windows operate. I am leaving the negative cable off overnight and see what the morning brings.

I did save the old alternator. If I don't get over 13 volts in the morning, I'll swap out the regulator.

rimutakaman · Post by **rimutakaman** » 18 Jul 2016, 20:35

So then it was the battery causing your electrical system to go haywire. I'm sure the electrical components will be fine in the morning, but I suspect the problem will reappear, i.e. you will have a weak battery once again after driving the car around for a bit. If what I said turns out to be true, the question then will be, what is bad -- is the alternator or regulator bad? or is your battery bad from being drained while the previous alternator was in the car?

You can check the alternator output with a multi meter, and if it is bad, then dwindle the problem down to see if the regulator is the issue. You can check the battery with a battery load tester.

Faust · Post by **Faust** » 18 Jul 2016, 22:40

If it helps, my reference to the "bad alternator period" does not mean that the old alternator was bad. What happened was that the alternator pulley failed. I replaced it with a used alternator from a T6, complete with pulley. Went mad for a couple of days trying to figure why the belt wouldn't go back on,. Seems the T6 alternator had a larger pulley. After figuring that out, I got the belt spec'd for the T6 and it went right on. I used the cooling fan removal theory to get the alternator out. Thaat means a number of electrical connections, I'd best check them.

difflock54 · Post by **difflock54** » 18 Jul 2016, 23:05

Had the same problem back in March with my V40.
The alternator appeared to be working and no charge failure warning light showing but the battery was gradually draining to below 9 volts.At that point everything started to fail including fuel pump and all dash gauges.
The alternator pulley was the initial problem but it had eventually damaged the alternator. New alternator with new pulley and all has been great since. Charges at 14.2 - 14.6 volts now and the battery was also okay once recharged.
The pulley can seize up or become partially seized resulting in the alternators failure.

Faust · Post by **Faust** » 19 Jul 2016, 11:51

I may have to turn in my car credentials. After spending a lot of time in the rear of the car with my multi meter, I decided to have a look in the front with an eye towards replacing the regulator. I immediately found that I had some how knocked loose the small wire to the alternator. Plugged it and got 13.5 volts at the battery.

rimutakaman · Post by **rimutakaman** » 19 Jul 2016, 14:55

Nice work! I'm fairly sure nearly everyone has neglected to tighten something, left tools in the motor, or something like that over the years in one form or another. Glad you got it working.

Post by **abscate** » 20 Jul 2016, 08:00

Submit your car credentials for the "Mistake Number 666" stamp. I ran out of space on mine for stamps a while back.