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Failed Xbee 3 LTE-M/NB-IoT after running for a few months.

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Hello all, anyone have issues with their Xbee 3 LTE-M/NB-IoT modems failing in the field? I have a few running L0.0.00.00.05.11,A.02.16 and Digi firmware 11417 that have stopped transmitting in the field. Upon checking the modem with an XBIB-CU-TH board, all cellular-related data is blank whereas before it was all there. Checked the SIM in another known, working modem and it's fine. When issuing a AT+CGSN results in "ERROR" along with all the other cellular network-related commands.

Also it is known that the modem can get in to an error state if a "Safe shutdown" isn't initiated prior to pulling power. I am using this modem in micropython mode and am issuing an "Airplane Mode" before shutting the modem down. Would like to know why this is happening and how to go about troubleshooting the issue if it only occurs every couple of months...
asked Aug 2 in XBee3 Cellular by samson49 New to the Community (10 points)

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2 Answers

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Samson49, you need to use the Shutdwon or SD function before you power off the module.
answered Aug 4 by mvut Veteran of the Digi Community (14,807 points)
0 votes
samson49 - Were you able to identify what the problem was? Was the u-blox module dead?
answered Aug 7 by acpie360 Community Contributor (75 points)
Indeed it was "bricked", meaning no cellular-related info to include the IMEI and it's not recoverable through a ublox firmware re-load. As for the problem, we are being told by Digi that all modems that end up in this state are due to messed up flash memory caused by an unsafe shutdown.  

We were using the "Airplane Mode" to safely shut down the modem as outlined in the Xbee manual but evidently that's not cutting it.  The only actual working method of safely shutting down the modem is to use the "SD" command which is contrary to the manual.  

Unfortunately Digi doesn't see this issue as a real problem because only 0.01% have failed this way.  This just tells me that most of their users are not cyclically powering down their modems to save power.  If they were, they'd have a lot more of these failures.
Thanks for the response.

Cross referencing with the u-blox SARA-R4 UG
---
Due to the nature of Flash memory, the Embedded File System (EFS) may incur memory corruption if
the safe & graceful shutdown procedure outline in the SARA-R4 series system integration manual [3]
is not followed. It is possible that memory corruption may result in the device being inoperable or
impact specific device data info.
---
Unfortunately, this particular model, SARA-R410M-02B-01, used in the Digi LTE-M/NB-IoT modem doesn't seem to have the EFS backup and restore feature. I am guessing when Digi picked the u-blox module for their modem design, they probably weren't aware of or paying enough attention on this issue.
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