> 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/controllers/controller-6000/troubleshoot/controller-6000-i2c-bus-not-responding.md).

# I2C Bus Not Responding

Diagnose and resolve Controller 6000 I2C bus communication failures before upgrading.

The 6000 controllers feature **three Supercaps** on the board, designed to keep the processor operational while the controller powers down.

## Symptom

| Field            | Value                                                       |
| ---------------- | ----------------------------------------------------------- |
| Error            | `I2C Bus not responding` (in event viewer and alarm viewer) |
| Log Location     | Event Viewer / Alarm Viewer                                 |
| Source           | Command Centre Event Viewer                                 |
| Affected version | All                                                         |

## Cause

If the **I2C Bus** alarm or event appears in Command Centre, it likely indicates that the **Supercaps on the controller have leaked**, which affects the Bus chip.

This issue has been known to cause additional problems, especially in controllers that have been **upgraded to the Linux version**.

## Resolution

> ⚠️ **Hardware fault, not a software fix.** Return the controller to repair, or replace the controller.

Before upgrading a site of C6000 controllers from WinCE to Linux, check the Command Centre alarm log for **"I2C Bus not responding"** messages. Controllers with this fault should be **replaced before the WinCE to Linux upgrade**, as they have been known to cause issues during upgrade. See [Upgrading, Downgrading, Defaulting and Compatibility](/knowledge-hub/products/cc-hardware/controllers/controller-6000/configure/controller-6000-upgrading-downgrading-defaulting-compatibility.md) for the upgrade-prep checklist.

***

🔗 **Related**

* [Upgrading, Downgrading, Defaulting and Compatibility](/knowledge-hub/products/cc-hardware/controllers/controller-6000/configure/controller-6000-upgrading-downgrading-defaulting-compatibility.md). Pre-upgrade checks.
* [NAND issue](/knowledge-hub/products/cc-hardware/controllers/controller-6000/troubleshoot/controller-6000-nand-issue.md). Another hardware fault to check before upgrading.


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