# C263A21 Index Mark Validation Failed

Alarm codes · `C263A21` · verification: source checked

The absolute motor encoder position cannot be validated because the joint encoder's calculated motor position is invalid. The code includes a signed value.

## Specification

| Property | Value |
|---|---|
| Code | C263A21 |
| Meaning | Validation of the detected index mark failed because the motor position calculated by the joint encoder is invalid, so the absolute motor encoder position cannot be validated. |
| Remedy | Perform a complete reboot sequence, update the software, or contact your local Universal Robots service provider for assistance. |

## Connected

- Controllers: [Universal Robots e-Series Control Box](https://machineschema.com/controller/universal-robots-e-series-control-box.md)

## Sources

1. [C263 Motor Encoder](https://www.universal-robots.com/manuals/EN/HTML/SW5_26/Content/prod-err-codes/topics/CODE_263.html) (accessed 2026-10-26)

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