ABB Jokab Pluto — Locating a Fault by LED & Reset

ABB · advanced · 30 min

On an ABB Jokab Pluto safety-PLC network, the LED pattern points straight at the faulted unit: solid red is the culprit, downstream units flash red/green, upstream stay solid green. Read the fault code in Pluto Manager.

⚠️ Pluto runs your safety program — a fault takes the machine safe. Use the LED pattern to find the exact unit, read its fault code, fix the real cause (often a two-channel discrepancy), then reset.

Find the faulted unit by its LED pattern

An ABB Jokab Safety Pluto safety-PLC network can chain up to 32 Pluto units, and its diagnostics make the faulted unit obvious at a glance:

• The unit with the error shows a solid red LED — that's the one to work on.
• Downstream devices flash red and green (they can't run because an upstream unit faulted).
• Upstream devices remain solid green (they're fine).

So walk the bus: the last solid-green unit is healthy, the first solid-red unit is the fault location, and everything after it flashes red/green.

Read the input/output LEDs and the fault code

• The Input and Output LED status gives additional detail — an LED on indicates an error on that channel, pointing you at the specific I/O.
• Connect Pluto Manager (the Ladder-Logic-with-function-blocks programming/diagnostic tool for Pluto) and read the fault code. ABB publishes a Pluto Message and fault code list that maps each code to its cause and action — use it for the exact meaning.

Fix the cause

Pluto works with traditional dual-channel safety devices, so many faults are:

• Two-channel discrepancy — the two channels of an E-stop/guard input disagree (one made, one not, beyond the allowed time). Inspect both channels and their wiring; both must switch together.
• Input/output wiring fault on the channel whose LED is on.
• A device fault on a connected safety component.
• Communication/bus fault between Plutos in the network.

Reset

Once the cause is eliminated, clear the fault per the fault-code list's action — typically the input discrepancy or device condition clears and the reset/start condition in your Pluto program allows the outputs to re-enable. Because Pluto supports hot-swap, a genuinely failed unit can be replaced in the field without reprogramming the rest of the network.

Step-by-step

1. Walk the LEDs — find the solid-red unit (fault location); upstream is green, downstream flashes red/green.
2. Read the Input/Output LEDs on that unit — an LED on flags the errored channel.
3. Connect Pluto Manager, read the fault code, and look it up in ABB's Pluto fault code list.
4. Fix the cause — two-channel discrepancy, I/O wiring, a device fault, or a bus/comm issue.
5. Reset per the fault-code action; re-validate the safety functions before production.

Never do this

Don't bridge a safety channel or bypass a device to clear a Pluto fault. The two-channel and cross-monitoring checks exist to catch exactly these faults; fix the real cause and re-validate.