Have electrical issue that I can't pin point down (electrics bamboozle me a bit). Hopefully you smarter people can figure this out. Net of it is, car has died randomly a few times which is dangerous and need to solve this.

I'll describe my observations and we can go from there:

1) Bought 2003 Volvo XC70. Previous owner hadn't driven it more than 500km in the last 3 years. No issues with electrics, battery was in seemingly good condition
2) 3months in, car wouldn't start one morning, battery dead (I'm sure I didnt leave anything on, but maaaaybe. Makes me think alternator)
3) Replaced battery - car fine.
4) A while later I left the country for a few months, not driving car over winter. Asked friend to start and drive it every now and then. He did, and the last time he started it before I got back was 4weeks prior.
5) Returned, the new battery really dead. Weird to happen again.
6) Charged up and was fine again.
7) Noticed head lights flickering subtly every now and then when driving in the dark - (I thought this would be the alternator?)
8) Car died randomly, mid drive. All lights came on the dash, lost power steering. Pulled over, put car in park, turned car off. Turned back on and started immediately (I also thought this could be alternator, but the fact that it started immediately has me suspicious)
9) The above happened again with same results. Car died mid drive, turned off and back on.


Electrics are a minefield to me but my thinking went from a bad circuit/fuse drain causing the battery to die, to a bad alternator causing lights to flicker and car to die. But I'm not so sure because the car starts back up well which means the alternator could be working fine?

I'm stumped on my next step.

 

You can't leave the car for a month or two without a battery maintainer or the battery disconnected. Starting the car and running for a few minutes does not recharge the battery enough.

Your stalling/stopping running - I would check for codes in all systems. VIDA would be best, but there are other quality scan tools available. One possibility is a problem with your CEM, the central electric module. Those normally malfunction when hot after driving for a while - I don't know if those conditions would be applicable in your case.

And you are correct - if the alternator stops charging - the engine will stop running when the battery goes dead. Before that happens the CEM will try to turn everything else off that is using current - in an effort to keep the engine going. If the alternator were bad/not charging - there would be no current to spin the engine over on the restart.

If it happens again the starter will work in neutral - so you don't have to come to a stop to engage the starter.

 

I actually like electrical problems.

Volt meters are very cheap and make a ton of sense. The electrical system on cars like this, non-hybrid, relatively simple voltage across the battery should look like so:

• resting voltage about 12.5
• engine running voltage about 14-ish; charging rate will be very high just after cranking.
• cranking voltage maybe 10, but hopefully 11.5.

​​​​​​​When the car is sitting, of course, electricity is being used to maintain memory and run the security system and clock, and the battery will discharge over time. "months" is a very very long time. Way too long.
If you are driving along with the alternator off, then the voltage will have to drop pretty low for the engine to actually stop, but it eventually will, because the PCM will just quit working. I have observed this multiple times, although not on my volvo. The battery won't be dead when this happens, but for sure, you won't crank it back up. You can bet your life on that. The voltage cranking will be far lower than whatever it was when the PCM quit working.

So if you want to be sane, spend $5 on a volt meter that fits in the cigar lighter. That's easy. You need to figure out why it died. It didn't die from low voltage, I promise. Ignore that possibility and recognize that you have a problem there that you really need to figure out.

 

Thanks for the super quick reply. Appreciated.

My friend did drive the car when I was away in order to keep it turning over, not just starting it (as that may actually do more harm then good without a proper drive/recharge). The net of it is, I think the time I spent away shouldn't of been the reason for issues with a new battery - of course I know very little so tell me if I'm wrong!

Good idea to check codes. Is there actually a difference in quality machines? I did a basic code check a while ago on a friends basic bluetooth app/plug and that only returned an emissions code which isn't a worry for me right now (fuel cap or sensor somewhere I guess). Maybe its worth me taking it into a mechanic to get this properly scanned.

What codes should I be looking for? What indicates the CEM? Is that something I can replace myself with a bit of YouTubery?

Thanks for the tip in neutral, makes sense.

 

So if I did get a volt meter, this would help determine battery/electrical issues in certain states? What if nothing is out of the ordinary there, would that narrow it down to something playing up intermittently?

 

1. with key off, measure voltage across the battery terminals. A fully charged battery will be in the 12.8V range, 12.6 at 80% charge. A drained battery will be 12.2V or lower. If your battery is showing say 10V or so, it means there's a bad cell. Now start the car up and again measure across the battery terminals. With the voltage should be in the 14V range. Now turn on some accessories - high beams, rear window defogger, AC blower, AC-DC on the stereo (loud). Measured voltage should stay over 13.5V give or take. This will tell you if the alternator is producing enough current to keep the battery charged. Final test is to measure current drain. First make sure you have the radio code handy. with the car off, disconnect the battery's negative terminal. Put your meter in current mode to measure milliamps (say zero to 1 amp etc). put the positive connector on the ground cable and the other connector on the battery post. You should see something smallish like less than 25mA of current draw with the car off. if you see more, then its time to start pulling fuses to see if you can isolate which devices are staying powered. Usually its something like a vanity light (glove box, mirror etc) not turning off.

 

Mate thank you for this detailed explanation. This makes a lot of sense and will have a play this weekend.

 

A 2003 takes a while to shut all the electronics down - if you unlock the car and open the trunk to disconnect the battery - Several modules will have powered up. It really takes an inductive ammeter and lots of patience waiting for modules to shut down to test for a drain on a canbus car.

Earlier cars - 1998 and older could easily be tested with an inline (wired in series) ammeter. Try that with a newer car - and you will easily blow the fuse (usually 10 amp) in the ammeter - and be very frustrated waiting for module to shut down.

 

I think there is extreme clarity about two major things of interest. The biggest point of clarity is that if the alternator shuts off, it's brazenly blatantly obvious. You should never be confused at all about the alternator being on or off. In practice that's like a 1 to 2 volt difference. Also, if a cell in the battery shorts out, the resting voltage of the battery will be nominally 10 instead of nominally 12. You'll never be at all confused about that either.

Other things that happen with voltage are a little more nuanced, maybe.

Just be warned here that new-ish cars will allow the PCM to control the alternator so that it shuts off to improve fuel economy and maybe if everything is perfect it'll kick on with a high charging rate only when braking. That's a feature.