Update — March 24, 2026
After a month of working this through email support, forum threads, and direct contact with Quectel’s engineering team, here’s where things stand:
Modem firmware situation:
Matas confirmed that the latest modem firmware Teltonika has on file is the same A01 build that shipped with the device — RG520NEBDCR03A01M4G_OCPU_02.200.00.000. Nothing newer available on their end.
However, Quectel’s own field application engineer confirmed two critical things:
- The OCPU firmware builds are Teltonika’s builds based on Quectel’s QuecOpen SDK — they are not Quectel firmware. Teltonika owns the build and release process.
- The A01 base revision is classified in Quectel’s release notes as pre-mass production firmware for engineering samples. The current production revision is A05 (RG520NEBDCR03A05M4G), four revisions ahead, with a substantial changelog.
This was previously documented by another TRB501 user in thread #16393, where Quectel directly told them A05 is current and Teltonika’s support team (Marija) offered a remote session to perform the update.
What this means:
The path to updated modem firmware requires Teltonika to rebuild their OCPU package against the A05 SDK base from Quectel. This isn’t something end users can do, and Quectel has explicitly warned against flashing non-OCPU firmware on TRB501 devices.
Bridge/passthrough mode:
Justinas from Teltonika confirmed in thread #18074 that R&D is aware of the bridge mode performance issue — traffic in bridge/passthrough mode goes through the device’s firewall rather than bypassing it, cutting throughput by 2-3x. No ETA on a fix.
Other TRB501 users seeing the same issues:
Since my original post, several more threads have appeared with TRB501 users on the same A01 modem firmware hitting modem crashes (thread #18183 — 90-second reboot loops in 5G mode), bridge mode throughput caps (thread #17601), and speed regressions after device firmware updates (thread #18394).
I’ve escalated the modem firmware issue to Teltonika’s sales and engineering contacts and have Quectel’s engineering team CC’d. Will update this thread when there’s progress.
If you’re a TRB501 owner experiencing similar issues, check your modem firmware version in the WebUI — if it shows RG520NEBDCR03A01M4G, you’re on the same pre-production build.