Pilz PNOZmulti Fault LED — Program Mismatch Recovery

Pilz · intermediate · 25 min

A red FAULT LED on a Pilz PNOZmulti base unit often means the safety program on the chip card differs from the program in the base unit. Here is the correct procedure to accept the new program.

⚠️ You are working on a safety device. Only accept a program you know is the correct, validated configuration for this machine. After any change, the machine's safety functions must be re-validated per your risk assessment.

Why the FAULT LED is on

A PNOZmulti configurable safety system stores its user program in two places: on the chip card and in the internal memory of the base unit. On every startup the PNOZmulti compares the two. If the program on the chip card is not identical to the program in the base unit, the base unit lights its red FAULT LED and does not go to the safe operational state.

So a FAULT LED right after a card swap, a program download, or a base-unit replacement almost always means: the card and the base unit are carrying different programs, and the unit is waiting for you to confirm which one to use.

Confirm the diagnosis

  • Normal ready state: POWER and RUN LEDs on the base unit (and READY) are lit continuously.
  • Fault state: FAULT is lit; the DIAG LED and the base-unit display carry the detail. Read the display — a program-mismatch condition is the classic cause, but the display distinguishes it from I/O faults (IFAULT / OFAULT).

Accept the new program — display method (units with a display + rotary switch)

  1. Switch off the supply voltage to the PNOZmulti.
  2. Insert the chip card that contains the correct new user program.
  3. Switch the supply voltage on.
  4. When the display shows the project name and "Accept?", press and hold the rotary switch down for about 5 seconds, then release.
  5. The base unit copies the card program into internal memory; on the next start the two match and the FAULT LED clears.

Accept the new program — link method (units configured for it)

  1. Switch off the supply voltage.
  2. Insert the chip card with the new program.
  3. Insert a link between output OA0 and input i19.
  4. Switch the supply on and wait for the DIAG LED to flash yellow.
  5. Switch the supply off, remove the OA0–i19 link, then switch the supply back on.
  6. The unit now runs the accepted program and the FAULT LED clears.

If FAULT stays on

If the LED remains red after accepting a program, re-read the base-unit display: a genuine IFAULT / OFAULT (input/output fault) points to field wiring or a shorted/open safety I/O rather than a program mismatch. Resolve that channel, and if the fault is unexplained, consult Pilz support — never defeat a safety output to clear a fault.

After the fix

Because you changed the safety program, re-validate every safety function affected (E-stop, guard, light curtain response) before returning the machine to production, and record it per your validation procedure.

Key points

  • The PNOZmulti compares the chip-card program with the base-unit program at every startup; a mismatch lights the red FAULT LED.
  • Ready state = POWER + RUN (+ READY) lit steadily; read the base-unit display to confirm the fault is a program mismatch, not IFAULT/OFAULT.
  • Display method: power up with the correct card, then hold the rotary switch ~5 s at the 'Accept?' prompt.
  • Link method: bridge OA0 to i19, power up until DIAG flashes yellow, power down, remove the link, power up again.
  • IFAULT/OFAULT instead means an input/output wiring fault — and any safety-program change must be re-validated.

Codes and symptoms

FAULT — Program mismatch (typical)
The user program on the chip card differs from the program in the base unit's internal memory; accept the correct program to clear.
IFAULT — Input fault
A fault on a safety input channel — inspect field wiring and the connected safety device.
OFAULT — Output fault
A fault on a safety output channel — inspect the output wiring and load; never bypass to clear.