Fanuc Alarm 435 — What It Means
Fanuc Alarm 435 indicates a servo following error on the Y-axis — the difference between the commanded position and the actual encoder feedback position exceeded the allowable tolerance during movement. Like Alarm 414 (X-axis) and 436 (Z-axis), this is a servo system alarm that indicates the Y-axis cannot keep up with the commanded motion profile.
Common Causes
- Y-axis mechanical binding — A worn linear guideway, over-tightened ballscrew preload, or interference in the Y-axis travel causes resistance that the servo can’t overcome within tolerance.
- Servo drive fault — A degraded or failing Y-axis servo amplifier reduces available torque, causing lag in position tracking.
- Encoder cable fault — A damaged or intermittent encoder cable causes the position feedback to drop out, instantly creating a following error.
- Parameter error — If the in-position tolerance or following error threshold parameters have been changed, the alarm can trigger at lower error values than previously acceptable.
Step-by-Step Fix {#fix}
- Jog the Y-axis by hand — With power off (E-stop engaged), try to move the Y-axis by hand. It should move smoothly with no rough spots or binding. Resistance indicates a mechanical issue.
- Check Y-axis servo drive status — Power up and check the servo amplifier display for the Y-axis. Any fault codes on the amplifier itself narrow the diagnosis to the drive or motor.
- Inspect the encoder cable — Check the Y-axis encoder cable from motor to drive for pinch points, cuts, and secure connections at both ends. Substitute a known-good cable to eliminate it.
- Check the Y-axis ballscrew and guideway — Look for contamination, inadequate lubrication, or visible wear. Ensure lubrication system is functional and oil levels are correct.
- Reset the alarm — Press RESET on the control panel after correcting the root cause. MDI jog the Y-axis through its full travel and confirm 435 does not return.
Parts Often Needed
| Part | Notes |
|---|---|
| Y-axis encoder cable | Amazon | Replace if damaged or intermittent |
| Y-axis servo motor | Amazon | Replace if motor resistance tests show winding fault |
| Y-axis servo amplifier | Amazon | Replace if amplifier shows its own fault code |
When to Call a Pro
Guideway and ballscrew repair requires precision measurement and Fanuc-trained service to restore machine accuracy after any mechanical work.