From the service manual:
A critical firmware error has occurred. This type of error can be caused by invalid print commands, corrupt data, or invalid
operations. In some instances, electrical noise in the cable can corrupt data during transmission to the MFP. Other causes include poor quality parallel cables, poor connections, or specific software programs.
1 Turn the MFP off, and then turn the
2 Upgrade the firmware.
3 Try printing a job from a different software program. If the job prints, go back to the first program and try printing a different file. If the message appears only with a certain software program or print job, contact the software vendor for assistance.
4 If the message persists when using different software programs and attempting specific print jobs, disconnect all of the cables that
connect the MFP to the network or a computer.
5 Turn the MFP off.
6 Remove all DIMMs and flash-memory cards. Do not remove the firmware memory card that is in slot 1.
7 Remove all of the EIO devices.
8 Turn the MFP on.
9 If the error message disappears, reinstall each DIMM, flash-memory card, and EIO device individually, making sure to turn the MFP power off and then on again as you install each device.
10 Replace the component that caused the error message.
11 If the error persists, replace the formatter.
To upgrade firmware:
The MFP has remote firmware update (RFU) capability. Use the information in this section to upgrade the MFP firmware. The overall process involves the following steps:
1 Determine the current level of firmware that is installed on the MFP.
2 Go to the HP Web site and find out whether a firmware update is available. If an update is available, download the latest firmware to your computer.
3 Transfer the new firmware from your computer to the MFP.
Determining the current level of firmware
To determine the current level of firmware, view the configuration information on the MFP control panel. To view the configuration information, follow these instructions.
1 Press MENU.
2 Touch INFORMATION.
3 Touch PRINT CONFIGURATION. The configuration page prints.
4 The firmware datecode is listed in the section called Device Information. The firmware datecode has this format: YYYYMMDD XX.XXX.X. The first string of numbers is the date, where YYYY represents the year, MM represents the month, and DD represents the date. For example, a firmware datecode of that begins with 20040225 represents February 25, 2004.
Downloading the new firmware from the HP Web site
To find the most recent firmware upgrade for the MFP, go to www.hp.com/go/lj4345mfp_software. This page provides instructions for downloading the new firmware version.
Transferring the new firmware to the MFP
This procedure requires that you install HP Web Jetadmin Version 7.0 or later on the computer. See Using HP Web Jetadmin software. Complete the following steps to update a single device through HP Web Jetadmin after downloading the .RFU file from the HP Web site.
1 Start HP Web Jetadmin.
2 Open the Device Management folder in the drop-down list in the Navigation panel. Navigate to the Device Lists folder.
3 Expand the Device Lists folder and select All Devices. Locate the MFP in the list of devices, and then click to select it.
If you need to upgrade the firmware for multiple HP LaserJet 4345mfps, select all of them by pressing the Ctrl key as you click the name of each MFP.
4 Locate the drop-down box for Device Tools in the upper-right corner of the window. Select Update Printer Firmware from the action list.
5 If the name of the .RFU file is not listed in the All Available images box, click Browse in the Upload New Firmware Image dialog box and navigate to the location of the .RFU file that you
downloaded from the Web at the start of this procedure. If the filename is listed, select it.
6 Click Upload to move the .RFU file from your hard drive to the HP Web Jetadmin server. After the upload is complete, the browser window refreshes.
7 Select the .RFU file from the Printer Firmware Update drop-down menu.
8 Click Update Firmware. HP Web Jetadmin sends the selected .RFU file to the MFP. The control panel shows messages that indicate the progress of the upgrade. At the end of the upgrade
process, the control panel shows the Ready message.
Using HP Web Jetadmin software
HP Web Jetadmin is a Web-based software solution for remotely installing, monitoring, and troubleshooting network-connected peripherals. The intuitive browser interface simplifies crossplatform
management of a wide range of devices, including HP and non-HP printers. Management is proactive, allowing network administrators the ability to resolve printer issues before users are affected. Download this free, enhanced-management software at www.hp.com/go/webjetadmin_software.
To obtain plug-ins to HP Web Jetadmin, click plug-ins, and then click the download link that is next to the name of the plug-in that you want. The HP Web Jetadmin software can automatically notify
you when new plug-ins are available. On the Product Update page, follow the directions to automatically connect to the HP Web site.
If installed on a host server, HP Web Jetadmin is available to any client through a supported Web browser, such as Microsoft Internet Explorer 6.0 for Windows or Netscape Navigator 7.1 for Linux. Browse to the HP Web Jetadmin host.
Replacing the formatter
1 Slide the formatter cover toward the left side of the MFP and remove it.
2 Remove two thumb screws (callout 1).
3 Slide the formatter toward the left side of the MFP, and then remove it.
NOTE Dislodging the formatter might require considerable force.
I hope all this information helps! Thanks and please take a moment to give this solution a rating of fixya.