Model facts that change the troubleshooting path
HP lists automatic two-sided printing plus Ethernet and USB connectivity for LaserJet Pro 4001dn.
HP positions the model as a professional black-and-white laser printer with Wolf Pro security settings.
Test matrix
What to test and what a pass actually tells you
Run the test closest to the symptom. A passing result narrows the diagnosis; it does not certify the entire device.
A repeatable defect on a controlled reference is stronger evidence of a printer/driver path problem than a single bad document.
→A repeatable defect on a controlled reference is stronger evidence of a printer/driver path problem than a single bad document.
→A repeatable defect on a controlled reference is stronger evidence of a printer/driver path problem than a single bad document.
→A repeatable defect on a controlled reference is stronger evidence of a printer/driver path problem than a single bad document.
→A pass proves this browser can reach DeviceOK through the current network path; link negotiation and router counters require OS/router evidence.
→Diagnostic focus
Problems worth separating on this model
Evidence handoff
If the browser cannot reach the suspected subsystem
Keep the browser result as one observation, then move to the operating system or manufacturer diagnostic that can see the protected hardware state. Do not interpret an unsupported browser API as a failed component.
For model-specific firmware, drivers or service diagnostics, use the official HP source linked on this page.