Hi everyone

Hoping for some help with diagnosing an electrical issue with my MY2017 XC90-II D5 Momentum. The battery in my XC90 keeps going flat if I don't drive it for a day or two. At first I just thought it was an old dying battery so I replaced that (and the start/stop battery at the same time as that's been needing replaced for a while). But after I left the car for a couple of days the new battery too was completely flat.

I've started doing some investigating - I've connected up a multimeter in series with the negative terminal of the main battery and been watching the current draw. With the car unlocked and everything off (after waiting a good 30 minutes for all the interior lights etc to go off) the current sits at about 0.9 amps. 10 watts or so of power. And every couple of minutes it spikes up to 2.4 amps, sits at that for maybe 15 seconds and then drops back down to 1.8 amps and then 0.9 amps before repeating this cycle. Clearly drawing 10-30 watts of power while the car is turned off is what is draining my battery so quickly.

The car doesn't have a whole lot of extras - winter pack (heated front seats, windscreen and steering wheel) and rear climate controls about the only electrical extras beyond the basics in these cars. The fuse boxes look pretty barren due to all the optional equipment that was not specified! I've experimented with pulling a few fuses out to see if it affects the current draw with no success yet - heated windscreen, power seats, seatbelt tensioners, AWD control, tailgate, tailgate foot sensor.

Does anyone have any suggestions what to look for next? The car runs and drives fine with no error messages coming up (except for the Volvo On Call thing needing service, but it's been saying that for the last 6 months without issues). I don't have an OBD scanner - would that be likely to show up any codes or errors that the car itself isn't showing me?

The car is not long back from the dealership where it got a new turbo (£5500 ouch). This issue began fairly soon after it came back from there, but fairly sure the battery was holding charge for the first week or two after we got it back so I don't think that will be connected?

Any advice for next steps would be much appreciated!
Jimmy

 

To look for a parasitic draw, you can do a lot with a standard amp-volt-ohm meter - even a $20 harbor freight clamp on unit will do the job. To start, its best to check if your charging system is doing the job.

1) engine off, check battery voltage across the terminals - should be 12.6 to 12.8. A drained battery will be down to 12.2 or less. 2) start the car and with the engine running measure the voltage across the battery terminals at idle - should be something in the 14 to 14.5 V range. Check if it goes up when you add some RPMs to the idle. 3) now turn on all the accessories - high beams, rear defogger, AC blower etc. check the voltage again - should stay above 13.5V

If all that checks now, now turn off the car and use the clamp meter to measure mA's on the main battery (red) cable. If you see say more than 50 or 100 mAs, then you have a parasitic draw. Start with the obvious - are the interior vanity lights off? Remove anything plugged into the lighter. Check glove box, trunk and under the hood lights to make sure they are turned off with the key off (you can use a cell phone to take a pic on a delay or you can pull the bulb(s) out or press the switch off by hand etc. Next is to go to the fuse box(es). Again with the key off, start pulling fuses to see if anything bumps down the current draw. Not sure of the exact spec but I'd suspect it should be less than 20 mAs when the car is off. You can also pull relays out as well to see if that de-energizes a circuit. Once you find the relay/fuse then you can research what devices are on that service path. Last would be to unplug the CEM but that can be a PITA on some models so you may just want to stop with the fuses and get help from a pro at that point.