A PowerFlex 527 drive (Bulletin 25C) is configured in Studio 5000 Logix Designer and commanded by a Logix controller over EtherNet/IP with integrated motion, so its faults are motion-axis exceptions rather than the F-numbers of a PowerFlex 525. When the drive faults or is inhibited, the LCD scrolls a message such as INIT FLT S03 – NVMEM CHKSUM: fault type, code, then a short description (
What is different on the 527
- Start, stop, direction and speed come from Logix motion instructions, for example MDS (p. 40). Configuration needs Logix Designer version 24.00 or later (p. 54).
- Limits, tolerances and fault actions are axis properties in Logix Designer (pp. 61, 113). The LCD and keypad show states and faults and set the network configuration (p. 40); the factory IP address is 192.168.1.180 (p. 47).
- STO is either hardwired (terminals S1, S2 and 01) or controlled over the network by a GuardLogix or Compact GuardLogix safety controller (pp. 54, 85, 91).
How to read the message
| Prefix | Meaning in the manual |
|---|---|
FLT Sxx, FLT Mxx |
Standard runtime axis exceptions |
INIT FLT Sxx, INIT FLT Mxx |
Exceptions during initialization that prevent normal operation |
INHIBIT Sxx, INHIBIT Mxx |
Exceptions that prevent normal operation while the drive is active |
NODE FLT xx |
Exceptions that prevent normal operation of the drive |
NODE ALARM xx |
Reported to the controller only, no other action |
SAFE FLT |
Safe torque off faults (p. 86) |
Source: Fault Code Summary (p. 106). A message ending in FL means a factory-set limit was exceeded; UL means a user-set limit (p. 106). A boot fault during initialization shows as BFxxx, for example BF003 (p. 41). After power-up the display shows the device or axis state, for example CONN_TIMEOUT, DUPLICATE_IP, START INHIBITED or MAJOR FAULTED (p. 41).
Indicators: FAULT steady red means the axis is aborting or major faulted, or the safety supervisor is in Abort or Critical Fault (p. 110). NET flashing red means an Exclusive Owner connection timed out; NET steady red means a duplicate IP address (p. 111).
Common fault codes
| Display | What it means | What to check |
|---|---|---|
FLT S07 – MTR OVERLOAD FL |
Motor thermal model above its factory limit of 110 % | Command profile: lower speed or more time (p. 106) |
FLT S08 – MTR OVERLOAD UL |
Motor thermal model above the user limit | Command profile; the Motor Thermal Overload UL attribute (p. 106) |
FLT S10 – INV OVERCURRENT |
Inverter current above the hardware instantaneous limit | Motor power cable and windings for shorts, wire gauge, continuous rating, acceleration times (p. 106) |
FLT S16 – GROUND CURRENT |
Excessive ground current detected in the power stage | Motor power wiring and cable for shorts; replace the motor if it persists (p. 106) |
FLT S23 – AC PHASE LOSS |
One AC input phase lost while enabled | AC input voltage on all phases (p. 106) |
FLT S25 – PRECHARGE FAILURE |
DC bus did not reach its level after charging | AC voltage on all phases, input wiring; replace the drive if it persists (p. 106) |
FLT S34 – BUS UNDERVOLT UL |
DC bus below the user limit | Incoming AC level, glitches and line droop, UPS; the Bus Undervoltage UL value (p. 107) |
FLT S35 – BUS OVERVOLT FL |
DC bus above the factory limit for the configured input voltage | Deceleration profile of every drive on the DC bus; unplug the shunt connector and measure its resistance (p. 107) |
FLT S37 – BUS POWER LOSS |
DC bus below the Bus Power Loss Threshold for longer than the Bus Power Loss Time | Incoming AC level, glitches and droop, UPS (p. 107) |
FLT S41 – FDBK SIGNAL NOISE FL |
Too many noise-induced A/B state changes from the encoder | Feedback cable, connector and shield; vibration; HTL/TTL DIP switches on the |
FLT S54 – POSN ERROR |
Position error above Position Error Tolerance for longer than its time | Position loop tuning, feedforward, drive and motor sizing, motor power wiring (p. 107) |
FLT S61 – ENABLE INPUT DEACTIVATED |
Enable Input dropped while the power structure was running | Enable Input level and wiring (p. 108) |
FLT M19 – DECEL OVERRIDE |
Drive not following the commanded decel because it is limiting bus voltage | Bus Regulator Action setting, external shunt, AC line stability (p. 108) |
INIT FLT M22 – ILLEGAL ADDRESS |
Invalid IP configuration, for example IP and gateway identical; the drive switches to DHCP | Set a legal IP address, mask and gateway, then cycle power (p. 108) |
NODE FLT 01 – LATE CTRL UPDATE |
Several consecutive controller updates lost | Fewer devices on the motion network, topology, network equipment, shielded cable, signal wiring away from power (p. 109) |
NODE FLT 06 – LOST CTRL CONN |
Communication with the controller lost | Ethernet connection, controller and switch (p. 109) |
NODE FLT 09 – DUPLICATE IP ADDRESS |
IP address already in use | Choose an unused IP address (p. 109) |
NODE ALARM 01, 03, 04, 05 (late update, clock jitter, clock skew, clock sync) are alarms with the same network checks (p. 110).
Safe torque off faults
The manual states that the integrated STO is approved by TÜV Rheinland for applications up to PLe, Category 3 (EN ISO 13849) and SIL CL3 (IEC 61508, EN
| Display | Logix Designer message | Meaning and checks |
|---|---|---|
INHIBIT M05 – SAFE TORQUE OFF |
Start Inhibit – Safe Torque Off | Hardwired STO has disabled the power structure: safety input wiring, safety devices (p. 109) |
INHIBIT S05 – SAFE TORQUE OFF |
Start Inhibit – Safe Torque Off | Network STO has disabled the power structure: Ethernet cables and switches, safety devices (p. 109) |
SAFE FLT S09 - SS IN |
GuardStopInputFault | S1 and S2 in different states for more than 1.0 second: STO terminations, connector seating, +24 V, input states; reset and run a proof test (p. 86) |
SAFE FLT S01 - GUARD INTERNAL FAULT |
CPUWatchdogFault (LCD: Module Fault) | Internal STO failure: cycle power; return the drive for repair if it continues (pp. 86, 94) |
SAFE FLT S03 - GUARD GATE DRIVE FAULT |
SafeTorqueOffFault (LCD: Safety Fault) | Internal STO failure (STO Fault Type 3): cycle power, execute the STO function, return the drive for repair if it continues. Hardwired input energized in network safety mode (Type 104): remove power, remove any connection to the hardwired safety inputs, restore power; or, if hardwired STO is intended, reset the drive to out-of-box hardwired mode (pp. 80, 86, 94) |
FLT M28 – SAFETY MODULE COM ERROR |
SafetyModuleCommunicationErrorFault | Error communicating with the safety module: cycle power, replace the module (pp. 94, 108) |
INIT FLT M14 – INVALID SAFETY FIRMWARE |
InvalidSafetyFirmwareFault | Safety firmware incompatible or missing: cycle power, upgrade drive firmware (p. 108) |
To tell the two causes of SAFE FLT S03 apart, read the STO Fault Type with a MSG instruction (Get Attribute Single 0x0E, class 0x5A, instance 1, attribute 0x108): 1 No Fault, 3 Circuit Error, 102 Hardwired Input Discrepancy, 104 Hardwired Input in Network Mode (p. 84). After a drive is switched to network STO, SAFE FLT S03 can appear until the Safety Bypass jumper is removed with power off (p. 91).
The drive ships with the Safety Bypass jumper on S1, S2 and S+ and does not run without a safety circuit or that bypass wiring; if the jumper is lost, S1, S2 and S+ may be wired together (p. 79). Hardwired STO needs the drive in the out-of-box state, the jumper removed and the safety device on S1, S2 and 01 (p. 85).
Where the fault shows in Logix Designer
The safety status in axis tags is STANDARD data, which the manual says must not be used as part of a safety function (p. 81). Useful bits: AxisFault.GuardFaultStatus (hardwired STO fault), AxisFault.SafetyFaultStatus (network STO fault) and AxisSafetyState, where 8 or 51 means the out-of-box state (pp. 79, 81–82).
Exception actions are set in Axis Properties, Actions: Ignore, Alarm, Fault Status Only, Stop Planner, Stop Drive or Shutdown; Shutdown needs an explicit Shutdown Reset (pp. 113–114). Most FL faults, and some others such as S10, S16 and S25, allow only Major Fault; the UL faults, the feedback faults S41 and S43, and others such as S23, S37 and S54 also allow Ignore, Alarm or Minor Fault (pp. 114–115). INIT FLT codes occur before enable, so no stopping action applies (p. 113).
Checks, step by step
- Record before resetting: the full scrolled text, the axis state, the FAULT, MOD and NET indicators, and the message in Logix Designer.
- Power faults (S23, S25, S34, S37): measure AC on all phases and look for glitches or droop.
- S10: motor power cable and windings for shorts, wire gauge, acceleration times (p. 106). S16: motor power wiring and cable for shorts; replace the motor if it persists (p. 106).
- Regeneration (S35, M19): deceleration profile, shunt resistor, Bus Regulator Action.
- Network (NODE FLT 01, 06, 09; NET red): cables, switch, topology, unique IP address.
- Safety (INHIBIT M05/S05, SAFE FLT): safety device state, S1/S2 wiring and timing, STO Fault Type.
Clearing faults safely
Find and correct the cause first; do not defeat the drive fault circuits. Before working on the drive, measure the DC bus below 50 V DC or wait three minutes (p. 105). The fault text clears when the controller sends a Fault Reset and the fault is no longer active; if it is still active, it is posted again (p. 105). Whether the axis moves again after a reset depends on the controller program issuing motion commands (p. 40), and the manual warns that an uncorrected fault can cause uncontrolled machine operation (p. 105): follow the plant's permit and lockout rules.
- Hardwired STO: both inputs must be off for more than 1 second, then an MASR command resets GuardFault and GuardStopInputFault (p. 87).
- Network STO: SO.SafeTorqueOff must go 0→1 before SO.Reset goes 0→1; then a MAFR clears Axis.SafetyFault (p. 93).
- With network STO, motion direct commands issued while the safety controller is in Program mode bypass STO and allow motion once the user acknowledges the warning; Logix Designer then shows "Safe Torque Off Bypassed" (pp. 100–104).
When it is hardware
The manual says to return the drive for repair if these continue: FLT M26 – RUNTIME ERROR, INIT FLT S03 – NVMEM CHKSUM, INIT FLT M15 – POWER BOARD, NODE FLT 02 – PROC WATCHDOG, NODE FLT 03 – HARDWARE 00, SAFE FLT S01 and S03 (pp. 86, 108–109). A previously used replacement drive must be reset to out-of-box before it goes on a safety network (p. 94).
Before calling for support, record the display text, axis and device state, indicator states, hardware and firmware versions from "Version Info" (p. 42), the STO Fault Type if relevant, and what the machine was doing. For an engineer on site: breakdown support.
Frequently asked questions
How do I read a fault on a PowerFlex 527?
The LCD scrolls the fault type, code and a short description, for example INIT FLT S03 – NVMEM CHKSUM (
Why does a PowerFlex 527 show INHIBIT M05 SAFE TORQUE OFF?
Hardwired STO has disabled the power structure; INHIBIT S05 is the network STO equivalent (p. 109). Check the safety input wiring and the safety devices; without STO, the drive must be in its as-shipped configuration: safety control in the out-of-box state and the Safety Bypass jumper on S1, S2 and S+ (p. 79).
What is SAFE FLT S09 on a PowerFlex 527?
S1 and S2 were in different states for more than 1.0 second (p. 86). Both inputs must be off for more than 1 second before an MASR resets it (p. 87).
How do I clear a PowerFlex 527 fault?
Correct the cause, then send a Fault Reset from the controller; the text clears only if the fault is no longer active (p. 105). A fault set to the Shutdown action needs a Shutdown Reset (p. 114).
Sources
- Rockwell Automation,
520-UM002F-EN-E , PowerFlex 527 Adjustable Frequency AC Drive User Manual, 09/2025 — pp. 40–42, 47, 53–54, 61, chapters 4–6 (pp. 77–104), chapter 7 "Troubleshooting" (pp. 105–115)
Read 13 November 2026. This article paraphrases the sources and does not quote them; read the original documents before designing or working on a system. Links open the latest edition in Rockwell's literature library; page numbers refer to the edition cited.