What causes FANUC alarm 376?

Bit 1 of parameter No. 1815 is set to 1 but the serial encoder does not support absolute position detection. Bit 3 of parameter No. 2002 is set to 0, disabling the absolute pulse coder function on the servo drive. Absolute position detection is enabled in parameters but the encoder connected is an incremental type, not absolute. Parameter mismatch after replacing a servo motor or encoder without updating the corresponding drive parameters. Corrupted or incorrectly restored parameter backup applied to a machine with different encoder hardware.

How do I fix FANUC alarm 376?

1. Check parameter No. 1815 bit 1 for the affected axis. If the encoder is incremental, set bit 1 to 0 to disable absolute position detection. 2. Check parameter No. 2002 bit 3 for the corresponding servo axis. If using an absolute encoder, this bit must be set to 1 to enable the absolute pulse coder. 3. Verify the physical encoder type installed on the motor. Confirm whether it is an absolute or incremental encoder by checking the motor nameplate or wiring documentation. 4. If parameters were recently changed or restored from backup, compare the current parameter file against the original machine parameter sheet to find mismatches on parameters 1815 and 2002. 5. After correcting the parameters, power the control completely off and back on. If using an absolute encoder, you may need to perform a reference position return to re-establish the absolute position. 6. If the alarm persists after parameter correction, check the encoder cable and feedback connection for damage or loose connectors that could cause the drive to misread the encoder type.

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FANUC Controller

System · Intermediate · 30-60 minutes

Alarm 376

Fanuc Alarm 376 - SERIAL DCL: ILLEGAL PARAMETER

Alarm 376 SERIAL DCL: ILLEGAL PARAMETER occurs when there is a conflict between serial encoder (absolute position detection) settings and serial communication parameters. This typically happens when parameter No. 1815#1 is set incorrectly for serial absolute encoders, parameter No. 2002#3 is disabled when it should be enabled, or there is a mismatch between the configured absolute position detection function and the actual encoder type installed on the servo axes.

FANUCSystemIntermediate30-60 minutes

376

Fanuc Alarm 376 - SERIAL DCL: ILLEGAL PARAMETER

FANUC ALARM 376

Root Cause Summary

Alarm 376 SERIAL DCL: ILLEGAL PARAMETER occurs when there is a conflict between serial encoder (absolute position detection) settings and serial communication parameters. This typically happens when parameter No. 1815#1 is set incorrectly for serial absolute encoders, parameter No. 2002#3 is disabled when it should be enabled, or there is a mismatch between the configured absolute position detection function and the actual encoder type installed on the servo axes.

Causes and Fixes

1
Navigate to SYSTEM > PARAM and access parameter No. 1815. Check bit 1 setting. If set to 1 with incremental encoders or non-serial encoders, this will trigger the alarm.
2
Verify actual encoder type installed on servo motors. Check servo amplifier labels and encoder cable connections (serial encoders use specific connectors - typically JA4 for alpha series, separate from power).
3
If incremental or parallel absolute encoders are installed, set parameter 1815#1=0. If serial absolute encoders (Ai series or Bi series) are installed, verify parameter 2002#3=1 is also set.
Changing parameter 1815 requires power cycle. Ensure battery backup is functional before changing absolute encoder parameters to prevent position loss.
4
After parameter change, power cycle the CNC completely. Execute absolute position reset if using absolute encoders by going to SYSTEM > PMC > KEEP RELAY and setting the appropriate reference position return completion bits.

DIY Feasiblehigh confidence

Call a technician if:

·Parameter changes don't resolve alarm
·Hardware configuration uncertainty
·Absolute encoder replacement needed

Prevention

Maintain parameter backups before changes
Document hardware configuration changes
Verify parameter compatibility before enabling new functions

Common Mistakes

Enabling serial functions without proper hardware
Not cycling power after parameter changes
Mixing incompatible absolute position and serial communication settings

Related Alarms

375 377 380 2010

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