Applicable Systems
EFC
FEX
FEI
HNC
Symptoms
Communication phase downgrade detected. The master has commanded a phase downgrade (moving from a higher phase to a lower phase), which is not allowed during normal operation.
Possible Causes
- Master initiated phase downgrade during operation (should only happen during shutdown)
- Communication error causing false phase change command
- Master firmware bug or configuration error
- Drive received corrupted telegram interpreted as phase change
Troubleshooting Steps
- Step 1: Check the master controller diagnostic for phase change events
Master did not intentionally initiate a phase downgrade - Step 2: Verify communication signal integrity (check for EMI on the cable)
No EMI sources near communication cables; signal quality is good - Step 3: Check for firmware updates or bugs on the master that may cause false commands
Master firmware is up to date with no known bugs - Step 4: If the phase change was caused by communication noise, improve cable shielding
Improved shielding eliminates intermittent phase change commands
How to Reset
1) Check master diagnostic. 2) Verify signal quality. 3) Check master firmware. 4) Improve shielding if needed. 5) Reset fault.
Frequently Asked Questions
- Q: When is a phase downgrade legitimate?
Only during an orderly shutdown sequence: Phase 4→3→2→1→0. A downgrade during operation (while in Phase 4) is not legitimate and indicates a fault.
- Q: What is the correct shutdown sequence?
Master commands phase downgrades in order: 4→3→2→1→0. The drive acknowledges each transition. After Phase 0, the drive can be powered off safely.
Source: Rexroth IndraDrive HCS/HMS Fault Code List, Bosch Rexroth AG
Category: PLC & VFD