> For the complete documentation index, see [llms.txt](https://help.security.gallagher.com/knowledge-hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.security.gallagher.com/knowledge-hub/products/cc-hardware/readers/t-series/t-series-t20-firmware-upgrade-issues.md).

# T20 firmware upgrade fails

Resolve failed T20 firmware upgrades from version 1.x to version 4.x or later.

### Symptoms and cause

**Symptom:** Errors appear in the Connections tab of the T20, or in the Alarm Viewer, when attempting a firmware upgrade.

![T20 firmware upgrade error in the Connections tab](https://328339335-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F6bM8WhlBE9BYizPWJaPN%2Fuploads%2Fgit-blob-439e34de259d4bf4865a5480053c6dec497ea561%2FSECHUB-TSERIES-T20FIRMWARE-01-upgrade-error-connections.png?alt=media)

![T20 firmware upgrade error in the Alarm Viewer](https://328339335-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F6bM8WhlBE9BYizPWJaPN%2Fuploads%2Fgit-blob-81406bbf4823f747d6312421748efa73bb798deb%2FSECHUB-TSERIES-T20FIRMWARE-02-upgrade-error-alarmviewer.png?alt=media)

**Cause:** The T20 firmware is on version **1.xxx**, and the target firmware is version **4.xx or higher**. Direct upgrade from 1.x to 4.x is not supported.

### Affected terminals

T20 readers are affected if they have always used CardaxIV. Their serial number is older than **1420xxxxxxxx**.

### Resolution

1. Take the T20 reader to a system running **Command Centre version 7.20 to 7.60**.
2. Connect the reader to that system.
3. Upgrade the firmware to version **3.x** on that system.
4. Return the reader to the original site.
5. Reconnect and proceed with the upgrade to 4.x or higher.

> **The intermediate step via a 7.20 to 7.60 system is mandatory when the reader has never been updated past firmware 1.x.** The reader cannot bridge the major version gap in a single upgrade pass.

***

🔗 **Related**

* [T Series - T20 User Guide and Resolution](/knowledge-hub/products/cc-hardware/readers/t-series/t-series-t20-user-guide-and-resolution.md). The T20 terminal.
* [T Series - Non HBUS compatible](/knowledge-hub/products/cc-hardware/readers/t-series/t-series-non-hbus-compatible.md). Older CardaxIV-only readers.


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