interior noise while engine is off

[JayDee24ca]

Can some one enlighten me as to what would be causing the very quiet hum, like a small motor or fan running, that is audible when my 2008 XC90 is parked and not running? It seems to be coming from the center console area. It makes me wonder how much current is being drawn and how long the battery will last.
Thanks
JD

[mrbrian200]

I don't know what it is for sure, my '06 S60 makes a similar barely noticeable noise, sort of a buzzy hum, from the center console area after I shut the car off. But it goes away when the main relay shuts off a couple minutes later as the car goes into 'sleep mode' --when some accessory electronics, such as the power seats, no longer work again until you do something to wake the system back up, such as turn the key or open a door. I don't consider it a problem.
The '06 S60/'08 XC90 are both P2 platform after '05 the electrical systems are very similar. I would imagine on the '08 it should stop after a few minutes too. If it doesn't there might be a problem.

[oragex]

Another source is the small cooling fan located in the ECM box, right in front of the power steering reservoir. This little guy keeps turning a few minutes to cool down the two ECM modules. It gets noisier with age as it starts seizing a bit (worth checking it)

[JayDee24ca]

On this car, the noise is continuous. It sits for many days between usages, and the noise is noticeable at any time. Or so it seems. If opening a door might cause some of these systems to "awaken", perhaps I should leave the windows rolled down so that I do not need to open a door, after an extended period, to hear the sound.

[mrbrian200]

Opening the door or unlocking with the fob wakes the car up: so it may seem like something 'unnecessary' is being powered 24/7. Sit in it after removing the key from the ignition without touching anything. It's either 3 or 5 minutes. On my '06 a few of the bulbs have been switched out to LED (front side marker, city, puddle, license lamps). On the older cars because the lamp driver circuits weren't specifically designed for LEDs these bulbs retain a faint glow until the car goes into sleep mode/main relay is turned off. In my car this light buzz and the faint glow from the LED bulbs cut at the same time. Touching much of anything except controls on the radio, climate control, or the power seat adjustments wakes the system back up.

[JayDee24ca]

Thanks Mr. B200, that is what is going on alright. Your assistance is appreciated, as is that of others who posted.
JD

[oragex]

As above, something is not shutting down, these relays shouldn't go for more than 2-5 minutes. You may have a short or a stuck relay somewhere. I'd first check the alarm siren, very prone to melting it's circuit board - google up. Other than that, it would be finding a needle in a haystack. The downside is the battery is drained when the car is parked which may weaken the car battery in the long term.

[mrbrian200]

On my sister's XC90 the main relay stays on much longer than it does on my S60. I suspect the difference has to do with particular vehicle options on the XC90 (NAV + fob based automatic seat memory recall). I could see people perceiving these systems might never turn off on the XC90 but if you sit in there long enough without touching anything it does eventually power down - but it's closer to 5 minutes on the XC90 whereas on my S60 its about 1.

The buzz is coming from the climate control module and sounds to me like some sort of switching/PWM type power supply.

[precopster]

The XC90 2006 electrical system is a little more advanced than earlier P2s. Just the other day I left the key in the accessories position for more than 2 hours if I recall correctly and display said something like "battery low in power saving mode". Car still cranked and started.

I was surprised to find access to power seats without the key this morning after car was sitting overnight but as mbrian stated this may be activated by a door opening; pretty cool.