Alarm guide · Allen-Bradley · Updated October 2026
Allen-Bradley S45 alarm: Feedback Comm Fault
Allen-Bradley Kinetix 5500 fault S45 is reported as a feedback communication fault (motor feedback data loss). It points to the motor feedback path: a loose pin, a damaged cable, poor shield clamping, earthing problems or noise, and in some cases the motor feedback device itself.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
Allen-Bradley Kinetix 5500 fault S45 is reported as a feedback communication fault (motor feedback data loss). It points to the motor feedback path: a loose pin, a damaged cable, poor shield clamping, earthing problems or noise, and in some cases the motor feedback device itself.
Safe first checks
General guidance only. Follow the drive manual and your site's electrical safety rules. Power off, and let the DC bus discharge, before touching connectors.
- Power off and check the feedback connector pins at motor and drive.
- Check the shield clamps on the feedback and motor power cables.
- Keep the motor cable from being coiled near earth sources.
- Check earthing and bonding of the drive and motor.
- Check the drive firmware is current for your motor.
When to send it for repair
Send the motor when the fault follows it. The feedback device is tested, repaired or replaced and aligned. Check the exact fault entry on your drive, because some systems report the same loss under a different code.
See Allen-Bradley servo motor repair, encoder repair and servo drive repair.
Questions
Can I clear the S45 alarm and keep running?
A reset may clear it for a while, but a feedback alarm usually comes back until the cable, connector or encoder is fixed. Running with an intermittent feedback fault can stop the axis without warning, so find the cause first.
Is it the motor, the cable or the drive?
Swap with a known-good cable first, then swap the motor to another axis if you can. If the alarm follows the motor, send the motor. If it stays on the axis with a good motor and cable, send the drive. We test both when you are not sure.
How long does repair take?
Emergency repair is done the same day where the fault and parts allow, urgent in 3 working days and standard in 7 working days, counted from when the unit reaches our bench and the quote is approved. Every unit returns with a printed test report.
Can I get an exchange unit?
If we hold a matching unit, Servo Swap ships a tested exchange unit while yours is repaired. Mark "line down" on the request form and add the part number.
Brand names identify the units we repair. Star Automations is an independent multi-brand repair company and is not an OEM service centre.