What the 26012 alarm means

The drive reports a general servo fault for the given axis; it is usually paired with 26013 and points to the KPP/KSP power stage or its supply. We have built up many handled cases of this KUKA KRC2 / KRC4 / KRC5 (KSS) alarm, and usually the first on-site inspection tells us what is wrong.

Most common causes

  • Damaged KPP/KSP module or loose power connections
  • Low-voltage supply fault between CCU and KPP/KSP
  • Firmware issue on some KPP/KSP versions
  • Motor power cable fault
Field note: Confirm or rule out the first cause first — it is the situation we encounter most.

Step-by-step field fix

  1. Record the axis number and check the KSP/KPP status LEDs
  2. Check the low-voltage supply and connectors between CCU and the drive
  3. Inspect the motor power cable and connectors
  4. Update KPP/KSP firmware if a known-bad version is installed
  5. Replace the KSP/KPP module if the fault persists
Safety first: For KUKA 26012, 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. On site you may not carry out the first step yourself: Record the axis number and check the KSP/KPP status LEDs. Beyond that it is the DC bus and power stage work - leave it to a professional. On KUKA 26012: 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 26012 belongs to the drive & power stage family. On KUKA 26012 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 26012 at the smartPAD message window (KSS message numbers: 1xxx operator, 2xxxx drive) with KPP/KSP module LEDs.

The chain involved in KUKA 26012 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Bottom line up front: Damaged KPP/KSP module or loose power connections is the first suspect for KUKA 26012, but read it along the energy chain: Any link on this chain dropping voltage shows up at the end as a drive alarm, so order matters. We measure the mains first: more than 3% phase imbalance is enough to sag the bus under load, and plenty of bus over/under-voltage alarms are actually a grid problem wearing a robot costume. Mains fine, then the bus capacitors - bulged cases, weeping electrolyte or a lifted vent mean replacement; capacitance down 20% or more cannot hold the bus during braking. Last, the braking resistor: healthy values sit in the tens of ohms depending on rating, and an open or drifted resistor trips regenerative overvoltage directly.

Field notes on this page cover KUKA 26012 (General Servo Error (Drive N)); written by the Henghuan repair team, updated 2026-10-01.

Real Field Case

Machine: KUKA KR 16-2 (KRC4) (2016)

Symptom: A KR 16-2 raised 26012 (general servo error, drive N).

What we did: We read the specific drive number, measured the motor and cable for that axis and found a broken encoder-cable core, then replaced the cable and reset.

Result: The alarm cleared after replacing the encoder cable and it ran normally; about 3 hours.

Can't clear it yourself? Contact us for remote diagnosis

Tell us the alarm code, the model and what the machine was doing when the alarm appeared. KUKA 26012 is an everyday diagnosis for our engineers, and remote diagnosis (phone or video) costs nothing.

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Related Drive & Power Stage alarms

12005 — Ballast Resistor Temperature Sensor — Wire Disconnection 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) 26122 — KSP Braking Resistor Fault (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 26012 alarm mean?

The drive reports a general servo fault for the given axis; it is usually paired with 26013 and points to the KPP/KSP power stage or its supply. We have built up many handled cases of this KUKA KRC2 / KRC4 / KRC5 (KSS) alarm, and usually the first on-site inspection tells us what is wrong. KUKA 26012 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Damaged KPP/KSP module or loose power connections".

QCan I clear a KUKA 26012 alarm myself?

Whether KUKA 26012 clears on its own depends on the outcome of "Record the axis number and check the KSP/KPP status LEDs". Finish the flow with "Replace the KSP/KPP module if the fault persists" to confirm KUKA 26012 - do not skip it. If that step is clean, the second most frequent cause on KUKA 26012 is "Low-voltage supply fault between CCU and KPP/KSP". After clearing KUKA 26012, 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 26012, what spares do you bring on site?

The commonest causes we see on KUKA 26012 are "Damaged KPP/KSP module or loose power connections, Low-voltage supply fault between CCU and KPP/KSP, Firmware issue on some KPP/KSP versions", so we stock the van against those. For KUKA 26012 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 26012, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what KUKA 26012 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 26012 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.