Allen-Bradley (Rockwell Automation) PowerFlex 525 fault F081: DSI Comm Loss
Fault F081 on a PowerFlex 525 is DSI Comm Loss: communication between the drive and the Modbus or DSI master device was interrupted. The response is set by C125 [Comm Loss Action], and the timeout by C126 [Comm Loss Time]. It is a Type 2 fault.
Diagnose this with AI
Try Free Drive Diagnostic Upload a keypad photo, the fault history or a parameter export from your Allen-Bradley (Rockwell Automation) PowerFlex 525. InduQT compares the evidence and suggests the next useful checks.
When it happens
- Running under RS-485 (Modbus/DSI) control
- When the master is stopped, rebooted or put into program mode
- Intermittently with electrical noise near the comm cable
Likely causes and checks
1Cable, connector or termination problem
- Points to it
- Trips when the cabinet is opened or the machine moves; several drives on the same network fault together.
- Check
- Check the RS-485 cabling and connectors, and the Modbus/DSI settings and status in the drive.
2Master stopped or not polling
- Points to it
- Trips coincide with PLC or HMI download, reboot or program mode.
- Check
- Check the master’s state at the fault time and compare the polling interval with C126 [Comm Loss Time].
3Electrical noise
- Points to it
- Random trips that follow large loads switching nearby.
- Check
- Rockwell notes that connecting I/O terminals C1 and C2 to ground may improve noise immunity; also check cable routing against power wiring.
4Failed master, wiring or control module
- Points to it
- Trip persists with a known-good cable and master.
- Check
- Replace wiring, Modbus master device or control module per the manual’s action list.
Telling it apart
- F071 DSI Net Loss: control over the Modbus or DSI link was interrupted. F072/F082 are for a network option card. F073/F083 are the embedded EtherNet/IP adapter (PowerFlex 525 only).
- C125 = 0 “Fault” trips on loss; 1 coast stop, 2 stop per P045, 3 continues at the last commanded speed. Choose the action from a machine-safety review, not to suppress the fault.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| C125 | [Comm Loss Action] | Fault (default), coast stop, stop, or continue at last speed on loss of RS-485 communication. |
| C126 | [Comm Loss Time] | Time in communication loss before C125 acts (default 5.0 s). |
| F681 | [Comm Sts - DSI] | Status of the DSI/RS-485 port for diagnostics. |
Evidence to collect
- b007 with time stamp
- C125 and C126 settings
- F681 [Comm Sts - DSI] diagnostics
- Master device status and logs at the same time
- Cable routing and termination photos
Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.