Servo encoder alarm quick sheet
Common encoder and feedback alarms on Fanuc, Yaskawa, Mitsubishi and Siemens drives, what each usually points to, and what to check on the cable and connector first.
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Download PDFGuide · 6 min read · Updated October 2026
Servo encoder alarms on Fanuc, Yaskawa and Mitsubishi drives
Most servo encoder alarms fall into four groups: no communication, bad data, lost absolute position and battery. The codes differ by brand, but the first checks are the same. These are the common codes and what they usually point to; always confirm with your drive's manual.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
01Fanuc
Fanuc serial Pulsecoder alarms
| Alarm | Usual meaning | First check |
|---|---|---|
| SV0366 | Pulse miss inside the Pulsecoder | Contamination or a failing Pulsecoder |
| SV0367 | Count miss inside the Pulsecoder | Disc or electronics fault |
| SV0368 | Serial data error | Feedback cable, connector, coolant in the Pulsecoder |
| SV0369 | Data transfer error | Cable shield, noise, connector pins |
| Battery low or zero | Absolute position battery | Change the battery with power on, then check the reference |
02Yaskawa
Yaskawa Sigma alarms
| Alarm | Usual meaning | First check |
|---|---|---|
| A.810 | Encoder backup error | Battery or backup circuit; re-set up the absolute encoder |
| A.820 | Encoder checksum error | Encoder memory; may need encoder service |
| A.830 | Absolute encoder battery error | Battery voltage and cable |
| A.840 | Encoder data error | Encoder fault or noise |
| A.850 | Encoder overspeed at power-up | Shaft moving at power-up, or encoder fault |
| A.860 | Encoder overheated | Motor temperature, cooling, encoder fault |
| A.C90 | Encoder communication error | Feedback cable, connector, shield, encoder board |
03Mitsubishi
Mitsubishi MR-J alarms
| Alarm | Usual meaning | First check |
|---|---|---|
| AL.16 | Encoder error at power-on | Cable, connector, encoder board |
| AL.20 | Encoder error during operation | Cable movement, noise, encoder board |
| AL.25 | Absolute position erased | Battery and battery cable; re-home |
| AL.92 | Battery cable disconnection warning | Battery connection |
| AL.9F | Battery warning | Replace the battery soon |
04Any brand
Checks that apply to every encoder alarm
- Read the full alarm history, not just the latest alarm
- Swap or test the feedback cable; most intermittent alarms are cable faults
- Look for coolant or oil inside the connector and behind the encoder cover
- Check the encoder supply voltage at the motor end
- Note whether the alarm comes at power-up, at speed or when the cable moves
- If the encoder was recently replaced, suspect alignment or memory
05Help
When to send it to us
If the alarm stays after a cable swap and a battery change, the encoder itself needs testing. Send the nameplate or WhatsApp +91 97866 22233. Related: Fanuc Pulsecoders, Yaskawa encoders, Mitsubishi encoders, absolute encoder batteries.
Free downloads for your maintenance file
Printable one-page sheets from our bench. More on the resources page.
Servo motor encoder quick reference
Encoder families, interfaces, counts per revolution and the motors they sit on: Fanuc pulsecoders (alpha A64, A1000), Mitsubishi OBA/OSA, Yaskawa UTOPH, Tamagawa, Heidenhain ECN/EQN/ERN and SICK SKS/SRS/SRM.
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Download PDF06Enquiry
Send the nameplate or encoder label
A clear photo of the motor nameplate and, if the cover is off, the encoder label is enough to start. We reply with whether it can be repaired and a quote.
Message received
Our team replies by email or WhatsApp, usually the same working day. For a line-down motor, WhatsApp +91 97866 22233.