Direct answer
When right travel, swing or arm movement is lost while other functions remain available, preserve the function pattern and the exact machine and valve identities. Informal descriptions such as “Black Knight” or a valve color do not establish a circuit specification.
Scope and safety
This is a symptom-recording and service-handoff guide, not a procedure for testing or adjusting the machine. Follow the exact machine manual and displayed safety instructions. Keep clear of moving equipment and suspected pressurized leaks. Shutdown alone may not remove stored pressure; hydraulic work and attachment support require the correct procedure and qualified personnel.
Make a function-by-function record
List the affected directions and which movements remained normal. Include the attachment mode, warning messages and recent control-valve or pump work. Keep observations separate from someone’s proposed explanation.
Label every pressure reading
If a qualified technician has already measured pressure, record the port designation, units, instrument and operating condition. A number labeled only “feedback” does not establish whether it was a pilot, load-sensing or another measurement.
Avoid changing the circuit to prove a theory
Do not move the breaker spool, exchange valves or adjust the pilot circuit as a workaround based on this article. Ask the service provider to identify the installed valve and trace the relevant diagram before selecting tests and parts.
Service handoff record
| Record | Information to supply |
|---|---|
| Identification | Full machine model and serial; engine or attachment identity where relevant. |
| Complaint | The affected function, direction, timing and original screen message. |
| History | Recent service, changed parts and existing test reports; mark missing information as unknown. |
| Diagnosis | Technician’s confirmed component, applicable manual reference and repair scope. |
Frequently asked questions
Does a response change prove a particular valve is faulty?
No. Record the change, but require a circuit-based diagnosis before replacement.
What identifies the correct control component?
The machine serial, installed valve or pump identification, full component number and the confirmed repair scope.
Sources and scope of evidence
- Hyundai Construction Equipment services and support — manufacturer documentation or support access; obtain the reference for your exact machine.
- Caterpillar hydraulic hose inspection and pressure safety — general hydraulic inspection and stored-pressure safety.
These public sources provide documentation/support routes and general safety context. They do not verify a model-specific fault-code definition, pressure setting or repair case. This guide therefore supplies no such specifications. Source links checked 14 September 2026.
Related guides
- Excavator Hydraulic Pump Failure Symptoms and Next Checks
- How to Check Parts Fitment Before an International Order
Parts identification after diagnosis
Danch Machinery supplies genuine parts. Send the confirmed part number, machine serial number and clear identification photographs for an availability and fitment inquiry. A symptom description does not establish fitment or current stock.
Request a parts identification check
About this guide
Published by Danch Machinery as general parts-identification and service-planning information. It is not a signed technical inspection or a machine-specific repair approval. Refer to the sources and scope stated in the article; confirm service procedures and fitment with the current manufacturer documentation for the exact machine.
Machine configurations and service requirements can differ by model, serial number and market. Confirm procedures and fitment with the current manufacturer documentation for your exact machine.
