Pin not connected

Diagnostic signature

Pin not connected

The KiCad Electrical Rules Checker (ERC) reports a "Pin not connected" violation when a schematic symbol pin is left floating without an explicit no-connect flag.

What it means

This diagnostic indicates that a pin on a placed schematic symbol does not have any electrical connections attached to it. The ERC engine requires all pins to be explicitly terminated or marked to ensure that floating inputs and forgotten connections are caught before layout. A pin is considered unconnected if it has no attached wires, power ports, net labels, or global labels, and it lacks a 'No Connect' (X) marker.

Why it happens

During the Electrical Rules Checker (ERC) validation, KiCad iterates through all symbol pins present in the schematic. The checker verifies the connectivity graph for each pin. If a pin is not part of any net and is not explicitly defined with an 'Unconnected' electrical type in the symbol library, the tool checks for a 'no-connect' flag on the schematic. If this flag is missing, the ERC engine assumes the omission was unintentional and emits the `[pin_not_connected]` violation.

Minimal reproduction

(kicad_sch (version 20231120) (generator "eeschema")
  (paper "A4")
  (symbol (lib_id "Device:R") (at 100 100 0) (unit 1)
    (in_bom yes) (on_board yes)
    (uuid "00000000-0000-0000-0000-000000000000")
    (property "Reference" "R1" (at 102 100 90))
    (property "Value" "10k" (at 100 100 90))
  )
)

How to fix it

Connect the floating pin to a valid net or explicitly mark it with a No Connect flag.

```KiCad Schematic
(kicad_sch (version 20231120) (generator "eeschema")
  (paper "A4")
  (symbol (lib_id "Device:R") (at 100 100 0) (unit 1)
    (in_bom yes) (on_board yes)
    (uuid "00000000-0000-0000-0000-000000000000")
    (property "Reference" "R1" (at 102 100 90))
    (property "Value" "10k" (at 100 100 90))
  )
  (no_connect (at 100 94.92))
  (no_connect (at 100 105.08))
)
```

Step 1

Locate the unconnected pin reported in the ERC dialog by clicking on the violation marker.

Step 2

If the pin belongs to a circuit path, use the Wire tool (W) or place a net label (L) to connect it to the appropriate net.

Step 3

If the pin is intentionally unused, select the 'Add a no-connect flag' tool (Q) and place the cross marker directly on the pin.

Upstream references

Schematic Editor | 8.0 | English | Documentation - Electrical Rules Checker

erc_settings.h - KiCad Source Code