Yaskawa GA800 E55 Fault — What It Means
The E55 fault on a Yaskawa GA800 variable frequency drive indicates a serial communication transmission error. The drive has detected a problem with the communication path and cannot see valid serial data. This is not a motor overload or input power issue. Instead, the fault points to a physical wiring or connection integrity problem on the serial communication cable itself.
Yaskawa’s documentation identifies three primary triggers for this code: incorrect wiring of the communications cable, a short circuit somewhere in that cable, or a disconnected or open cable. In practice, this means you are looking for a bad connection, a damaged wire, or terminals that have been swapped or miswired during installation or maintenance.
Before You Replace Anything
Technicians sometimes replace the communication option card or control board first. Always inspect and verify the physical communications cable wiring, terminations, and continuity before swapping boards.
Common Causes
- Incorrect communications cable wiring Conductors may be swapped, transposed, or landed on the wrong terminals during installation or after service work.
- Short circuit in the communications cable Damaged insulation, pinched wiring, or wire strands touching can create a short anywhere along the cable run.
- Disconnected or loose cable The communications cable may be unplugged, poorly seated, or have an open conductor due to a broken wire or loose terminal.
- Communication option card not fully seated If the system uses a network adapter or option card, the card may have vibrated loose or have bent pins preventing good contact.
- Damaged RJ45 or network connector For Ethernet or fieldbus options, a cracked connector, broken latch, or damaged jack can interrupt the link.
Quick Diagnosis
Answer these to narrow it down fast.
Is the communications cable visibly disconnected or loose at either end?
No: Proceed to inspect the cable routing for damage, pinch points, or signs of a short along the entire run.
Does the system use a communications option card or network adapter?
No: Focus on the direct serial cable wiring between the drive and the host controller or PLC.
After re-seating connections and verifying wiring, does the E55 fault persist?
No: The fault was caused by a loose or incorrect connection. Document the corrected wiring and return the drive to service.
Step-by-Step Fix
- Verify the fault code displayed on the drive keypad and confirm it reads E55, not a different communication alarm.
- Power down the drive and lock out the incoming supply before inspecting any wiring or connections.
- Inspect the communications cable at both ends for loose terminals, disconnected plugs, or visibly damaged insulation.
- Check the cable routing along its entire length for pinch points, sharp bends, or areas where the insulation may be compromised or shorted.
- Re-seat or reconnect the communications cable, making sure conductors are landed on the correct terminals according to the wiring diagram.
- If an option card is present, power down, remove the card, inspect for bent pins or debris, re-seat it firmly, and verify network connector integrity.
- Restore power to the drive, clear the fault using the keypad reset procedure, and monitor for recurrence. If the fault returns immediately, replace the communications cable or escalate to Yaskawa support for board-level diagnostics.
Parts Often Needed
| Part | Notes |
|---|---|
| Communications cable (serial or network) | Amazon | Match the cable type, length, and connector style to your drive and host controller. Verify shielding and grounding requirements per Yaskawa wiring guidelines. |
| Communication option card (e.g. SI-EN3 Ethernet card) | Amazon | Only replace if the card is visibly damaged, has bent pins, or if cable inspection and re-seating do not resolve the fault. |
When to Call a Pro
Call a qualified industrial controls technician or Yaskawa-certified service provider if you are not trained to work on VFD communication systems, if the fault persists after verifying and replacing the cable, or if you suspect the drive control board or option card has failed. The GA800 troubleshooting manual emphasizes limited field repair beyond specific replaceable components, and Yaskawa support should be consulted for board-level diagnostics or firmware-related communication issues. Do not attempt to modify communication parameters or replace internal boards unless you have the proper training and access to Yaskawa’s elementary diagrams and service documentation.
Rough cost: A pro service call runs about $150-400.