What the 26122 alarm means

The KSP reports a fault in the braking resistor circuit for the axis — regenerative energy cannot be safely dissipated. We are very familiar with this alarm on KUKA KRC2 / KRC4 / KRC5 (KSS) systems — usually the first on-site inspection is enough to confirm the cause.

Most common causes

  • Open-circuit ballast resistor
  • Broken resistor wiring or terminals
  • Faulty braking chopper in the KSP
  • Resistor overheat tripping its temperature sensor
Field note: Our ticket data shows the first cause is by far the most common — start there to avoid dead ends.

Step-by-step field fix

  1. Measure the ballast resistor resistance and compare with specification
  2. Inspect resistor wiring and terminals
  3. Check the 12005 sensor circuit
  4. Replace the resistor or the KSP chopper stage as indicated
Safety first: For KUKA 26122, this alarm family involves the DC bus, which sits at several hundred volts and stays charged for minutes after power-off - touching terminals is a shock hazard. What you can check yourself first is Measure the ballast resistor resistance and compare with specification; the DC bus and power stage handling is not a DIY job. On KUKA 26122: checking incoming voltage at the disconnect and looking at breakers and fuses is fine to do yourself; opening the cabinet to touch bus terminals or pulling power modules needs a qualified electrician.

How we diagnose drive alarms on site

KUKA 26122 belongs to the drive & power stage family. On KUKA 26122 the failing stage is KPP power packs and KSP servo packs (next-generation drive modules on KRC5) on the KRC2 / KRC4 / KRC5 - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading KUKA 26122 at the smartPAD message window (KSS message numbers: 1xxx operator, 2xxxx drive) with KPP/KSP module LEDs.

The chain involved in KUKA 26122 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

When KUKA 26122 fires, the site usually reports Open-circuit ballast resistor first, but the real cause is often cooling: More than half of power-stage alarms are not a dead device but a device cooked by failed cooling. A stopped cabinet fan, a packed filter mat or a dusted air duct keeps IGBT junction temperature high: intermittent over-temperature first, hard fault days later. On these alarms we open the power module and look for cracked thermal paste and felted dust in the duct, then measure phase-to-phase output and insulation to frame. Swapping the module without cleaning the duct just buys the same failure again.

Field notes on this page cover KUKA 26122 (KSP Braking Resistor Fault (Axis N)); written by the Henghuan repair team, updated 2026-10-01.

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Related Drive & Power Stage alarms

12005 — Ballast Resistor Temperature Sensor — Wire Disconnection 26012 — General Servo Error (Drive N) 26013 — General Inverter Failure (Drive N) 26107 — KSP DC Link Overvoltage (Axis N) 26108 — KSP DC Link Undervoltage (Axis N) 26111 — KSP Device Overtemperature (Axis N)
Same family: this code belongs to the Drive & power stage alarms family - the page collects all Drive & power stage-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for ABB · Yaskawa · Universal Robots and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the KUKA 26122 alarm mean?

The KSP reports a fault in the braking resistor circuit for the axis — regenerative energy cannot be safely dissipated. We are very familiar with this alarm on KUKA KRC2 / KRC4 / KRC5 (KSS) systems — usually the first on-site inspection is enough to confirm the cause. KUKA 26122 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Open-circuit ballast resistor".

QCan I clear a KUKA 26122 alarm myself?

Whether KUKA 26122 clears on its own depends on the outcome of "Measure the ballast resistor resistance and compare with specification". Finish the flow with "Replace the resistor or the KSP chopper stage as indicated" to confirm KUKA 26122 - do not skip it. If that step is clean, the second most frequent cause on KUKA 26122 is "Broken resistor wiring or terminals". After clearing KUKA 26122, watch it for one shift. A second trip means stop and let an engineer arrive with the right test gear for the DC bus and power stage.

QFor drive/power alarms like KUKA 26122, what spares do you bring on site?

The commonest causes we see on KUKA 26122 are "Open-circuit ballast resistor, Broken resistor wiring or terminals, Faulty braking chopper in the KSP", so we stock the van against those. For KUKA 26122 specifically, we stock the van along the energy chain: braking resistors, bus capacitors, input fuses, drive-board supply parts and the common power modules for the brand. For KUKA 26122, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what KUKA 26122 shows on the smartPAD message window (KSS message numbers: 1xxx operator, 2xxxx drive) with KPP/KSP module LEDs and what the machine was doing - phone or video triage is free.

The content on KUKA 26122 was written by Henghuan Robotics service engineers from hands-on repair experience. Alarm descriptions are our own reference summary and may differ by controller or software version — defer to KUKA documentation, or contact us to confirm. Henghuan is an independent service provider with no affiliation or endorsement by KUKA.