S60 & other P2 Volvos: Troubleshooting Alternator & Electrical

MVS Volvo Forum user coflynn shows us step-by-step how to diagnose annoying, battery-killing electrical drains that leave you stranded:

My car was completely flat today. CAA came & boosted me, as part of that they do a little diagnosis, where they said the car was drawing ~4.5 amps when off, which is much too high. Everything else came back OK, and the car would still charge fine.

I thought I’d share my troubleshooting tips/strategy for anyone else who runs into this.

You will need the following to work on this:

• Clamp multimeter that measures DC current, ideally with diode test functionally
• Good sized tool kit… lots of fiddling with different sized screws etc
• List of good swear words

#1) When checking the drain current, clamp around the negative cable. Turn everything off, lock the car. You can trick the trunk into thinking it’s locked by pushing the round part of a screwdriver into the trunk latch.

#2) Measure the current. It takes ~20 mins for the car to enter full standby, where the current should be something like 50mA (your meter may not even measure that low). However in my testing it would drop considerably within ~30 seconds of locking. If the current is still pretty high then it’s probably not an issue of waiting to enter standby.

#3) From the battery, there are two leads. One goes off to the left and into the main distribution box, the other goes straight to the front for the starter + alternator. Clamp each of these at a time (may need to move battery a bit), and figure out which your drain is coming from. If going to the front, don’t bother pulling fuses in the back/cabin/etc as it won’t do anything.

#4) If your drain is coming from somewhere cabin, you could pull fuses one at a time to see when it goes away. There is a fuse box in engine compartment, passenger compartment (driver side), and trunk. I would be cautious pulling fuses for the computers, and start with the more obvious ones (lights, etc). 

#5) If drain is coming from the front, it is probably going into the alternator. If the car is cold you can see if the alternator is hot, assuming you have a fairly substantial draw (e.g.: 4A @ 12V = 48W… something will be warm). You may wish to confirm this by UNHOOKING THE BATTERY, disconnect the top cable from the ‘jump start’ location in the front (see photo below), reconnect the battery, and check the current readings again. Here I’ve insulated that terminal to ensure it doesn’t spark back on.

You can also (and should) use a current clamp to check the lead going into the alternator. It’s critical the clamp meter closes all the way or the reading is garbage. Will take some fiddling if you have a bigger clamp:

S60 Battery Drain / Standby Current + In-Place Alternator

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Last Updated on June 14, 2024