!!
critical HP
Error Code Error light on continuously (red LED blink pattern)
Severe error indicating hardware failure or system corruption.
? What Causes This
Printer failure due to internal damage or firmware issue.
✓ How to Fix It
Service repair and possible replacement is necessary.
Source: page 4 of the official manual
From the manual
This error code appears in:
HP Laserjet Mfp M139 M142 Printer