What causes FANUC alarm 086?

External computer or DNC software disconnected or lost the serial port connection. RS-232 cable has a broken or intermittent DR/DSR signal wire. DNC software timed out and dropped the connection. Serial interface board in the CNC lost the input signal. USB-to-serial adapter dropped the connection during transfer.

How do I fix FANUC alarm 086?

1. Check the DNC software connection status on the external computer. 2. Verify the RS-232 cable is fully connected and the DR/DSR line is intact. 3. Test the cable with a breakout box or multimeter if available. 4. Restart the DNC software and reconnect before retrying the transfer. 5. If using a USB-to-serial adapter, try a different adapter or a direct serial port.

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FANUC Controller

Program/G-code · Intermediate · 15-30 minutes

Alarm 086

Fanuc Alarm 086 - DR OFF

Fanuc Alarm 086 indicates corrupted or invalid data received during serial communication with an external device (DNC, robot, PMC I/O Link, etc.). This is typically caused by incorrect communication parameter settings, electrical noise on RS-232/RS-422 lines, or faulty cabling between the CNC and external equipment.

FANUCProgram/G-codeIntermediate15-30 minutes

086

Fanuc Alarm 086 - DR OFF

DR OFF

Root Cause Summary

Fanuc Alarm 086 indicates corrupted or invalid data received during serial communication with an external device (DNC, robot, PMC I/O Link, etc.). This is typically caused by incorrect communication parameter settings, electrical noise on RS-232/RS-422 lines, or faulty cabling between the CNC and external equipment.

Safety

Data not usable

Causes and Fixes

1
Navigate to SYSTEM > PARAM and verify parameter 0020 (channel selection: 0=RS-232C, 4=Ethernet), parameter 0100 (stop bits: 0=1bit, 1=2bits, 2=1bit even parity, 3=1bit odd parity), parameter 0101 (data bits: typically 7 or 8), and parameter 0102 (baud rate: 4800, 9600, 19200, etc.).
2
Compare CNC parameter settings with external device communication configuration documentation. Ensure exact match of baud rate, parity, stop bits, and data length.
3
Verify parameter 0000 bit 0 (TV check: set to 0 to enable parity checking) and parameter 0011 (input device code: typically 0=EIA/ISO, 2=EIA with no parity).
4
After parameter changes, power cycle the CNC completely. Test communication with a simple program transfer or MDI data send to verify data integrity.
Parameter changes require CNC restart to take effect. Backup parameters before modification.

DIY Feasiblehigh confidence

Call a technician if:

·Interface board replacement required
·Multiple parameter corruption detected
·Intermittent faults persist after cable/power verification

Prevention

Regularly inspect I/O cables for wear
Maintain stable power supply to peripheral devices
Keep backup of working parameter settings
Use proper cable strain relief

Common Mistakes

Assuming cable is good without continuity testing
Overlooking external device power requirements
Not checking parameter settings after battery replacement
Testing cables while connected to live CNC interface

Related Alarms

085 087 088

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