Code 126-0137: Too many I/O terminals present. Current: %1; permitted: %2
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical Too many I/O terminals present. Current: %1; permitted: %2 alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
[Cause of error] There are too many I/O terminals present on the PLB, MB, TE, UEC, or UMC units. Functionally safe terminals count as one terminal. Perhaps more terminals were detected than are actually present on the units. Some units contain internal terminals that are included in this count for technical reasons. [Error correction] - Modify the machine configuration in order to avoid exceeding the maximum number of terminals - Inform your machine manufacturer
Source: HEIDENHAIN NC Error Messages — TNC7/640/620/320/128, CNC PILOT 640, MANUALplus 620 (10/2023)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Heidenhain TNC Series CNC Alarms
Heidenhain controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 126-0137 on the TNC Series CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Heidenhain's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4497 Heidenhain TNC Series CNC codes.
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