Technical Tip: LTE modem firmware upgrade on FortiGate fails with message ‘Firmware Upgrade Timeout/Error!'

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Description	This article describes a known-issue where FortiGate models that have built-in LTE modems (such as the FortiGate-40F-3G4G and FortiGateRugged-60F-3G4G) are unable to successfully upgrade the LTE modem firmware when on certain FortiOS firmware versions.
Scope	v7.2.9.
Solution	There is a known-issue where LTE modem firmware upgrades will fail on the FortiGate with an error message stating ‘Firmware Upgrade Timeout/Error! Reboot modem and try to recover!’  Example output: execute lte-modem start-upgrade You are going to burn the following images into your LTE modem. --------------------------------------------------------- Modem image: 00005000MIMG00000.cwe PRI image: 02005000MIMG00000.nvu --------------------------------------------------------- The original images on your LTE Modem will be replaced! Do you want to continue? (y/n)y Starting LTE Modem firmware upgrade, please don't power off your device until the whole process is done! LTE Modem firmware upgrade routine will run in the background. FortiGate-40F-3G4G # . Reset modem to start upgrade! ..........................................................................................................................................................Firmware Upgrade Timeout/Error! Reboot modem and try to recover! Failed to restore original image! Modem will now reboot! This issue has been observed when the FortiGate is running FortiOS v7.2.9, though the issue may also occur on FortiOS v6.4.16, v7.0.13, and any later minor version (the issue is not present in FortiOS v7.4 or v7.6). The issue is being tracked by the Fortinet development team with ID #1005020 and it is resolved in FortiOS v7.2.11. This issue is fixed in versions 7.2.11, 7.4.4 and 7.6.0. Technically, the issue was introduced in interim versions of FortiOS v7.4.4 and v7.6.0 and then solved before they hit GA, so the issue 'never existed' for the GA versions of firmware. Workaround: Downgrade to FortiOS v7.2.8 and then upgrade the modem firmware (the issue is not observed on FortiOS v7.2.0 through v7.2.8). Once the modem is updated, upgrade the FortiGate back to FortiOS v7.2.9. Upgrade to v7.2.11 (Available to download on the Fortinet support portal). Related documents: 3G4G Modem Firmware Upgrade Guide Modem firmware download guide