Introduction: Why KUKA Error Diagnosis Requires a Systematic Approach
A stationary robot costs real money. Every minute of downtime in a production line can cost between $500 and $20,000 depending on the industry. Searching for the cause of a red KRC4 error without a systematic approach wastes valuable time. This article shows you how to correctly read KUKA error codes, understand the most common faults, and diagnose them efficiently.
Understanding the KRC4 Error System
The KRC4 controller distinguishes between three types of messages:
- Message: Informational, no stop required
- Warning: Program continues, attention required
- Error: Program stops, acknowledgment required
Every error has a unique number in the format KSS XXXXX. The first three digits indicate the error class; the last two identify the specific cause. In the KRC4 log (Menu → Diagnosis → Logbook) you can view the complete error history and filter by timestamp.
The 10 Most Common KRC4 Error Codes
1. KSS 00000 – Drive Not Ready
This error appears when the drives fail to initialize after power-up. Common causes: missing 48V supply, safety circuit not closed (E-STOP), faulty safety contactors in the KPS (power supply unit). First check the LED indicator on the KPS and the safety circuit diagnostics at Menu → Commissioning → Safety Controller.
2. KSS 00042 – Axis Velocity Exceeded
The robot has moved a programmed axis beyond the permitted maximum velocity. Causes: excessive override values during teach-in, incorrect tool data (overestimated inertia), or faulty path planning with zones too small. Solution: reduce override to 10–30%, check tool data with KUKA.Load.
3. KSS 01280 – Collision Detection Triggered
This is one of the most frequent interruptions in production environments. The KRC4 continuously monitors drive torques. When actual torques exceed the model-calculated values by a defined factor, collision detection triggers. The cause may be a real collision, but also: incorrect mass inertia parameters, startup issues with a cold gearbox, or overly sensitive thresholds. Thresholds per axis can be adjusted via $COLLISION_LIMIT[].
4. KSS 01301 – Calibration Required
You see this error after a machine reference point failure or when a resolver absolute encoder has lost its memory. Check the buffer battery in the controller (minimum 3V). After replacing the battery, every axis must be re-mastered. Use the EMD (Electronic Mastering Device) or the mastering gauge for precise results.
5. KSS 03510 – Drive Overtemperature
Thermal protection in the servo amplifier or motor has triggered. Causes: dirty or faulty fans in the control cabinet, too high a duty cycle (intensive application without sufficient cooling time), blocked airflow from cable routing, or ambient temperature above 45°C. Check temperatures at Menu → Diagnosis → Drive Status.
6. KSS 06022 – Fieldbus Communication Error
Connection to a PROFINET or EtherCAT device has failed. Check the network topology in WorkVisual, physical cable connections, and whether the affected device is visible on the bus. In the KUKA system: Menu → Display → I/O → Fieldbus shows the communication status of all configured devices.
7. KSS 00006 – Program Synchronization
The KUKA program could not synchronize with the PLC system. Typically occurs in systems with KUKA.PLC mxAutomation or external PLC solutions. Check communication parameters, timeout values, and whether the handshake signal is responding correctly.
8. KSS 00700 – Brake Test Required
After a configured number of operating hours or cycles, the system requires a brake test. This is a safety requirement per EN ISO 10218. The test can be performed in T1 mode and takes approximately 2–5 minutes. It checks whether each axis drifts unintentionally with brakes released.
9. KSS 01750 – Axis in Invalid Range
A software limit switch has been reached, or the programmed point is outside the reachable workspace. Check software limits at Menu → Commissioning → Configuration. In WorkVisual, workspace monitors can be configured to define certain zones as restricted areas.
10. KSS 02008 – Resolver Error
One or more resolvers (angle encoders) are reporting faulty signals. Causes: damaged signal cables (especially at cable drag chains), electromagnetic interference, connectors with oxidation. Locate the faulty resolver through the axis diagnostics. The logbook states the exact axis (A1–A6, or E1–E6 for external axes).
WorkVisual as a Diagnostic Tool
KUKA WorkVisual is much more than a programming tool. The integrated diagnostic function allows:
- Real-time monitoring of all axis data (torques, temperatures, velocities)
- Access to the complete error log with filtering functions
- Online adjustment of parameters such as
$COLLISION_LIMITor software limits - Log file export for offline analysis
Connect WorkVisual via the KLI interface (Port 8 on the KRC4 switch) to the controller. The default IP scheme is 172.31.1.147 for the controller.
Systematic Approach for Unknown Errors
When you encounter an unfamiliar error code, proceed as follows: note the code and timestamp. Check the logbook for adjacent warnings that preceded the error. Refer to the KUKA System Software documentation (located in the KRC4 filesystem at C:KRCROBOTERConfigUserMada). The error index often reveals the true trigger: the last displayed error is not always the first and therefore the root cause.
Conclusion
KUKA KRC4 errors can be resolved quickly with the right systematic approach. Most errors have well-known, recurring causes. Invest time in thorough documentation of your system, maintain correct tool and load data, and use WorkVisual as your primary diagnostic tool. For recurring errors, always examine parameter settings — causes are often overly tight thresholds or outdated calibration data.