Pixhawk LED Definitions?

I can’t seem to find any information on the LEDs on the front of the pixhawk, B/E ACT PWR etc. Does anyone know what these LEDs and their flashing signify?

Have a look here diydrones.com/profiles/blogs/pix … ector-demo might be of some help

Yeah I have looked high and low for those and can’t find them either. The moderator didn’t read your post carefully. You are not talking about the main LED, which is confusing enough, but are asking what are the 5 LEDs at the other end of the face of the Pixhawk. They are explained nowhere. There are 2 LEDs under FMU and 3 under IO. Pwr means power and is supposed to be green and on all the time under both categories. Both categories have B/E and I can not find any information on what the hell B/E means, what the lights should do, anything! On mine if I am under USB power and plug in a battery the B/E under FMU glows amber but seems dim. Both B/E seem to only be Amber and flash when I start the Pixhawk. Finally the third on below IO is Act which I think means activity and is Blue. I flashes all the time. Just a steady flash.

Moderator, Please note we are talking about the “other” LEDs on the face. By the way the content of the video you referred to is almost all the connectors and doesn’t explain the “Main” LED very well. It needs redone.

My problem with wanting to know about the “other LEDs” stems from my Pixhawk not loading the firmware and my Safety Switch flashing 4 times which means “IO not armed” — And? What do I do? How do I arm it? Help. Help. HELP, Please.


The LEDs are

FMU PWR = Flight management Unit Power
FMU B/E = FMU Processor in Bootloader mode (flashing) or Error (Steady)

I/O PWR = Input/ Output Power
I/O B/E = I/O processor in Bootloader mode (flashing) or Error (Steady)

ACT = Activity (a flashing heartbeat) indicating everything is ok

I’ll get that added to the documentation



Thanks for this info. It really helps to have some idea what those LEDs mean.

So when I plug my battery in and the B/E Amber light under FMU comes on and is steady, What does that mean?

And my safety switch flashes 4 quick flashes - IO not armed, I think - and I can’t get my PH to work. Is that because of a problem with my FMU (battery causes Amber LED) or IO (Safety switch flashes) ?? Or are these issues not important?

I have already sent an email to support but not heard back yet.

Thanks again


More info:
My Hex started working - Hard to say why but I am glad. The safety switch still flashes 4 times indicating IO not armed.

I got this info:
 Slow Blink: Ready to arm
 Fast Blink: Error / refusing to arm
 Long Off with fast double blink: IO armed, but FMU not
 Long Off with fast quad blink: FMU armed, but IO not
from here: http://pixhawk.org/users/status_leds

How can we use this info? Is there a place it is explained more fully? Right now our use is only ‘Steady Red’ means ‘armed.’ Anything else means ‘not armed.’

If the FMU is not armed can we arm it. If it is the IO that is not armed, can we arm it. Or does the fact that they are or are not armed mean something else? Or was this just a debugging tool for developers and should be ignored by us now?

Sorry to be such a pain.

And thanks again.


Hi Craig, thanks for the clarification there.
Now I have B/E solid on the IO side, together with ACT flashing. This means according to your explanation, error and everyhing OK at the same time?
ArduPlane 2.78b firm, PX4.

Your assumption is correct. My Pixhawk displays the leds the same way when the processor is running without any issues.

Hi, thank you. Yeah after a little while or after something else, the B/E LED went off!
Regards, Soren


I would appreciate any more information on these LEDs and what one can learn from different states.

If I connect my pixhawk (2.4) to my laptop I’ll get both power LEDs “on” and the ACTivity LED (I/O) flashing. However, if I attach the main battery the B/E for FMU is “on”. Seems to be not as bright as the other B/E (I/O) LED when flashing during initialization, but it is powered. But I can arm the device and get the motors running. I cannot do a flight test as the quad is not ready, yet :wink:.

Anyone able to give an explanation?

Thank you!

Same question here, after I plug in the battery pmu b/e led is on. What does this mean? But I can arm and run the motor. And all leds seems normal except for that b/e.

Same here, The FMU B/E led remains on , just a little dimmer, I would really like an explanation as to why.

Regards Peter

[quote=“Craig3DR”]The LEDs are

FMU PWR = Flight management Unit Power
FMU B/E = FMU Processor in Bootloader mode (flashing) or Error (Steady)

I/O PWR = Input/ Output Power
I/O B/E = I/O processor in Bootloader mode (flashing) or Error (Steady)

ACT = Activity (a flashing heartbeat) indicating everything is ok[/quote]

dev.ardupilot.com/wiki/interfaci … g-the-nsh/

Thankyou for posting those links…I have looked at them but have not found anything regarding the issue about FMU B/E led (PixHawk)

As Craig wrote, your PH runs into an error while in bootloader mode. To find out, into which exactly, you have to do debugging through the console.

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