Temperature controllers
Honeywell UDC2500 Digital Controller fault codes
What all 10 Honeywell UDC2500 Digital Controller fault codes mean, in plain words, with a risk grade for each. These come from the manufacturer's own manual. The fix for each one is in WERCS Diagnose.
Get the fixes · plans from $49/moUpdated November 4, 2026
| Code | What it means | Risk |
|---|---|---|
| 01 | Illegal Function The received message is not an allowable action, preventing the addressed device from executing the command. | YELLOW |
| 02 | Illegal Data Address The referenced data address is not valid, which stops the addressed device from processing the communication message. | YELLOW |
| 03 | Illegal Data Value The value referenced at the addressed device location is out of range, causing the command to fail. | YELLOW |
| 04 | Slave Device Failure The addressed device cannot process a valid message due to a bad state, halting communication with the controller. | YELLOW |
| 07 | NAK, Negative Acknowledge The addressed device cannot process the current message, which prevents the system from executing the requested action. | YELLOW |
| 09 | Buffer Overflow The requested data exceeds the available buffer space, causing the controller communication to fail. | YELLOW |
| LOCK | LOCK The lockout feature is enabled, which prevents unauthorized changes to certain functions or parameters on the controller. | GREEN |
| 05, 06 | Slave Device Busy The controller cannot communicate because the addressed slave device rejected a message due to being busy. | GREEN |
| PV LIM | PV LIM The process value is out of range, which causes the controller to stop regulating the booth environment. | GREEN |
| EE FAIL | EE FAIL The controller is unable to write to its memory, meaning any parameter changes will not be accepted or saved. | YELLOW |
Every code comes from the manufacturer's own manual. Subscribers see which manual and page.