Got an ASUS motherboard?  Are you having problems booting sometimes?  Do messages regarding ‘chassis intrusion’ get displayed on your screen, and stop the boot process, even though no-one has opened the case?  There might be a simple solution.

Chassis Intruded!
Fatal Error... System Halted.

The first time I got the above message I was a bit surprised.  I’m the only one that uses my computer, there are no kids in the house, and the case hadn’t been opened for months.  Pressing the Reset button resulted in a clean boot, so I wasn’t worried.  Computers do strange things sometimes and reboots make most of the problems go away.

But, it happened again a few weeks later, and again, and again…  Ultimately, a pattern emerged:  Whenever the power was cut to the computer for an extended period of time, the intrusion message would come up.

Sometimes I power off my computer from the wall for a few hours when a thunderstorm is rolling through.  Sometimes the LEDs on my stupid Steelseries keyboard will stay on even after the system has shut down, so I terminate power using the switch on the Power Supply Unit (PSU).  Sometimes I turn off power at the PSU when cleaning coolers and fans, installing solid state drives, and otherwise maintaining or tweaking the system.  Sometimes I go camping and power down the whole house (except the fridge) from the fuse box.

Opening the case wasn’t causing the error.  Physically cutting off power to the system was.

The only hunch I had was that it might have something to do with the battery.

Every motherboard has a small clock in it that keeps track of the time.  When the computer is connected to an AC outlet on a wall, the clock is powered by that.  When the power is physically cut (by turning it off at the wall or on the back of the PSU) then the clock is powered by a small battery on the motherboard instead.  If the battery is nearing the end of its life, and there isn’t enough power to keep the clock running, the clock will drift or reset, and when your computer starts up you are greeted with an operating system message telling you that your clock may be incorrect.  I’ve seen that happen many, many times over the years.

Even though I wasn’t seeing any clock symptoms here, I reasoned that something like a chassis intrusion system would need to monitor at least something while the power was disconnected, and if the battery was weak there may not be enough power for that circuit to operate properly.  Enough power for the clock, yes, but not enough for intrusion detection.  (Or it could be some obscure but related value stored in CMOS that was being wiped.)

So, whilst driving past Bunnings one day I popped in and picked up a pack of four CR2032 3V Lithium batteries for about $6.  When I got home I popped the case open, replaced the old battery with a new one, and closed it back up.  Only took a few minutes.  That night I shut down and terminated power to the system completely using the switch on the PSU.  The power was completely cut for over eight hours overnight.

In the morning I reconnected the power and booted the machine — everything worked perfectly.  No error message.  Nor has there been an error message for the days weeks months years since (even though I’ve had to cut power a number of countless times for various reasons).

Problem.  Solved.  🙂

If you are in the same situation — getting chassis intrusion messages when you boot, or clock errors, or any other symptom that seems to occur after cutting power to your system — then spend a couple of bucks and replace your motherboard battery before trying anything else.  It could be the fastest and cheapest hardware fix you ever get to perform.

Happy booting!

PS:  My motherboard is an ASUS Maximus IV Extreme-Z and was purchased in 2011.  Lots of other ASUS motherboards have the chassis intrusion feature, so I suspect will behave the same way when the battery starts to die.  Also, motherboards from other vendors like MSI, ASRock and Biostar probably have a similar feature on at least some of their boards.  I don’t consider this problem/fix to be motherboard-specific, or even vendor-specific.

PPS:  Motherboard batteries should last at least 3 years in a typical system that spends the vast majority of its time plugged into an AC outlet.  They will discharge faster in systems that are physically disconnected from external power frequently and/or for extended periods of time (e.g. because you use one of those ‘energy saving’ powerboards that cut power off completely when you press a button on a remote, or you’re in the habit of turning off your system at the PSU because it’s the only way you can get all of those motherboard LEDs to turn off at night so you can get to sleep, or the system is put into storage due to changing circumstances).  I’ve had batteries last over 8 years in servers that are continuously powered and running.

PPPS:  I tested the old battery with a multimeter.  The voltage of the cell was 2.26V.  This is well below the 3.0V ‘normal’ level, and getting quite close to the 2.0V threshold at which the performance of a CR2032 cell falls off a cliff.  It would seem that 2.26V is still enough for the clock circuitry to function normally, but not enough for the intrusion detection circuitry.