HP Printer Error Code 42 — What It Means & How to Fix It

What Does This Error Mean?

Error 42 on HP LaserJet printers typically indicates a problem with the printer's power supply or an issue with the duplex unit. The printer detected a mismatch or communication failure with an internal component. It can also appear after a firmware update does not complete correctly.

Affected Models

HP LaserJet 4200 Series
HP LaserJet 4300 Series
HP LaserJet 5000 Series
HP LaserJet Enterprise M600 Series
HP LaserJet Pro M700 Series

Common Causes

A duplex unit accessory is improperly seated or has a loose connector
The printer firmware was interrupted during an update, leaving it in a bad state
The printer is connected to an unstable power source or an incompatible power strip
An internal cable connecting a component to the formatter board has come loose
The printer was turned off abruptly during a print job, corrupting internal state data

How to Fix It

Turn the printer completely off using the power switch. Unplug the power cord from the wall outlet and wait a full 60 seconds.

This fully discharges the printer's internal capacitors and clears any stuck error states.
Check whether a duplex unit or any optional accessory is attached to the printer. Remove it, inspect the connector for bent pins or debris, then firmly reseat it.

The duplex unit is usually attached to the back or side of the printer. It should click firmly into place.
Plug the printer directly into a wall outlet — not a power strip or UPS unit. Then power the printer back on.

Power strips and surge protectors can sometimes deliver slightly different voltage that confuses HP printer power supplies.
Check for a pending or failed firmware update. On the printer's display, go to Setup > Printer Maintenance > Firmware Update.

If an update was interrupted, you may need to download the firmware manually from support.hp.com and reinstall it via USB.
If the error still appears, perform a cold reset. On most HP LaserJets, hold down specific buttons during startup (check your model's manual) to reset settings to factory defaults.

A cold reset will erase custom settings like paper trays and network configuration — make note of these before resetting.

When to Call a Professional

If error 42 persists after reseating accessories and power cycling, the formatter board or power supply unit may need replacement. These are internal repairs that require disassembly. An HP service technician can diagnose the exact component and provide a repair estimate.

Frequently Asked Questions

Is error 42 a serious problem?

It can be moderate to serious depending on the cause. If it clears after a power cycle and accessory reseating, the issue was likely a temporary communication glitch. If it returns every time you print, there may be a hardware fault that needs professional repair.

Can a firmware update cause error 42?

Yes. If the printer loses power during a firmware update — or if the update file is corrupted — the printer can get stuck in an error state. Visit support.hp.com, find your model, and download the firmware update tool to reinstall a clean version.

Does error 42 mean my printer needs to be replaced?

Not necessarily. Most error 42 cases are resolved by reseating accessories or reinstalling firmware. Only if the formatter board or power supply has physically failed would replacement be the likely outcome — and even then, a repair is often more cost-effective than a full replacement.