Is my S60 alternator dying?

Sardine · Post by **Sardine** » 02 Feb 2016, 03:36

My 2004 S60 2.5T alternator output is quite low. 13.0 - 13.7 during the day, 12.9 - 13.2 at night. This is what the OBD port tells me. There is nothing else wrong with the car, but will it leave me stranded someday soon? What do people think? If this is the symptom of a dying alternator then is it the bushes or the regulator? It is unlikely to be the diodes, right? Once I know, I will order the correct components online and keep them as spares for later. I always buy spare parts in advance as it takes a while to get stuff from the States to Australia.

MarcM · Post by **MarcM** » 02 Feb 2016, 05:06

Get a DMM. Set it for AC. Put across battery termunals. Anything more than 500mV AC (rule of thumb), the regulator has a diode heading south. You can get just the regulator (I *think* comes with brushes) for less $. Read somewhere the alternators sometimes sieze.

Post by **precopster** » 02 Feb 2016, 05:14

Measure the voltage AT THE ALTERNATOR positive post. If it's significantly higher you have corrosion in the B+ lead.

To alleviate this you can run an extra medium guage lead from the junction point near the fusebox directly to the alternator positive post.

Sardine · Post by **Sardine** » 02 Feb 2016, 22:41

Happy to report that the OBD port was lying to me. When I put on my DMM on the battery posts at the fuse box with the intention of doing the tests that MarcM and Precopster suggested, the voltage I read on the meter was jumping around 13.9-14.1 volt, while the scanner was saying 13.6. Since my meter is well calibrated, the car computer measurement is 0.4 Volt lower than the actual voltage. The AC component was ~50 mV by the way. When I turned the car off, the OBD port output was 11.4, the meter 12.1. People with a ODB reader may want to carry out the same test too see if this 0.4 Volt offset is true for other S60s, and V70 etc. When my wife gets home today, I'll have a look to see if her V70 is doing the same thing.

nsjames · Post by **nsjames** » 03 Feb 2016, 12:55

I am curious, is the voltage regulated by the PCM in the p2 platform? I don't know.

because a low voltage reading at the PCM can potentially over excite the alternator and cause an overvoltage situation.

It's probably prudent that you go ahead and clean all of the underhood electrical connections anyway.
Faulty grounds are cause for all manner of weirdness.

Sardine · Post by **Sardine** » 04 Feb 2016, 15:26

It looks like the 0.4 Volt offset is there in my wife's V70 as well. Since The V70 alternator output is higher, ~14.4 Volt, I've never notice anything strange in the OBD measurement of the battery.
nsjames: I don't know if the alternator output is regulated by the CPU. I've always thought that it is an open loop as far as the CPU is concerned. The alternator itself may have a feedback loop that regulates it's own output. What I'm going to do, as a matter of interest only now that I know everything is well, is to a look at the wiring diagram to see how the battery output is read by the CPU (CEM?) As this is a 10 year old car, the CPU may not have an internal A/D converter.

Post by **mrbrian200** » 04 Feb 2016, 15:56

OBD says 14.0v (engine running) on mine. I've been wondering about that myself whether it should be higher or if that's after a ECM internal regulation (that would make sense to be regulated a bit lower than alternator output voltage).

I had corrosion on mine at the B+ battery lead at the main breakout under the hood. Common problem on a lot of cars I fix it by soldering that crimp. It's approximately 00 copper wire crimped to a steel ring terminal I just solder them with a propane torch. You'll need more flux than electrical solder normally has "built in"- I have a small tub of flux (sold for plumbing work at any hardware store). Use lead free electrical solder,a bigger spool at least 8 oz. Just be careful not to get the wire too hot if you scorch it the copper oxidizes and solder won't stick. Slather with flux melt solder into it, repeat flux/solder until it fills in and looks good. Don't use leaded solder under the hood/exterior circuit repairs, between heat sublimation and salt corrosion leaded solder cant be trusted as a permanent fix.