No security updates since Nov 2015, and no Marshmallow update. How can I tell what is causing this?

[piratefan]

Subject says it all.

 

[jj14x]

What carrier SIM does your phone have?
What build do you have on your phone? (settings/about)
Did you buy your phone used? (to see if previous owner may have made changes)
Are you running a custom ROM? (custom anything?) Or are you fully stock?
Do you know if your bootloader is unlocked?
Have you ever performed a factory reset on your phone?

 

[piratefan]

Sprint
Android 5.1.1 (build# LYZ28N)
phone obtained as MotoCare replacement
fully stock
bootloader unlocked
I perform factory resets about every 6 months as a rule. This phone has been reset once.

 

[jj14x]

I believe LYZ28N was a T-Mo build (even though Google never called it that). With a Sprint SIM in it, it may be looking for a Sprint build, and because it doesn't find it on your phone, it doesn't prompt for OTA.

There are a few ways around this.

1. Try to remove your Sprint SIM, and factory reset, and let it boot up (without the SIM). From what I've heard, it will get you an update to the generic/unified Marshmalllow build - it may actually give you more than one OTA, first to get you to 6.0, and then, to get you to 6.0.1 followed by monthly builds. With 6.x, it is supposedly a unified build
2. If you can borrow a T-Mo SIM from somebody, you can swap SIMs and check for updates.
3. If you are comfortable with ADB sideload (doesn't require you to unlock bootloader), you can download the appropriate OTA file (that takes you from LYZ28N to a 6.x build), and use ADB sideload to load that (get URL from xda forums)
4. If you are comfortable with flashing factory images, you can skip all this drama, and unlock your bootloader, and flash the latest factory image and be done with it.

 

[mxmarcus]

With the bootloader unlocked you could flash the latest update no wipe to keep your data

 

[piratefan]

I ended up using Wug's Nexus Root Toolkit to flash the new update straight from Google's servers. It was super easy and I didn't have to use a command prompt!

[Toolkit] Wug's Nexus Root Toolkit v2.1.4 [U… | Nexus 6