HP Printer Error Code 78: How to Fix It

Medium 20-60 minutes Medium Severity Verified June 2026
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Error Code
78
Brand
HP
Product Type
printer
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
20-60 minutes
HP Printer Error Code 78 indicates that the image scanner (flatbed scan bar) has failed to return to or locate its home position during a startup or scan cycle. This typically happens due to a jammed or obstructed scanner carriage, a dirty scanner rail, or a faulty scanner motor or position sensor. The error is rated medium severity — the printer won't function until it's resolved, but in most cases it can be fixed at home without professional help.
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Tools You'll Need

How to Fix Error Code 78

  1. Power Cycle the Printer

    Always unplug from the wall outlet — not just from the printer — to ensure the device fully resets and to protect you from electrical hazards.

  2. Inspect the Scanner Glass and Carriage Area for Obstructions

    Do not press hard on the scanner glass — it can crack. Handle any debris carefully to avoid cuts on glass edges.

  3. Clean the Scanner Carriage Rail

    Unplug the printer before cleaning internal components. Never spray liquid directly into the printer — apply it to the cloth first.

  4. Lubricate the Scanner Rail

    Do not use WD-40 or cooking oils — these can damage plastic components and attract debris. Use only appropriate lubricants like white lithium grease.

  5. Manually Reset the Scanner Carriage to Home Position

    Never force the carriage if it feels stuck — forcing it can break the belt drive or damage the scanner motor. If there is firm resistance, move to the next step to investigate deeper causes.

  6. Update or Reinstall the Printer Firmware and Drivers

    Do not interrupt a firmware update once it has started — doing so can corrupt the printer firmware and require a factory service reset.

  7. Inspect the Scanner Position Sensor

    Opening the scanner housing may void your warranty. Proceed only if your printer is out of warranty and you are comfortable with disassembly. Take photos of each step before you begin.

  8. Perform a Factory Reset (Last Resort)

    A factory reset will erase all saved network credentials, custom settings, and any stored jobs. Record your Wi-Fi passwords and settings before proceeding.

Parts You May Need

Scanner home position sensor
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Scanner carriage drive belt
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Scanner assembly (flatbed module)
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Scanner home position sensor
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Scanner carriage drive belt
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Scanner assembly (flatbed module)
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Scanner home position sensor
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Scanner carriage drive belt
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Scanner assembly (flatbed module)
Check Price on Amazon
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When to Call a Professional

You should contact an HP-certified technician or HP Support if: (1) the scanner carriage is physically stuck and will not move even after cleaning and lubrication; (2) you can hear a grinding or clicking noise when the printer powers on, suggesting a broken belt or damaged motor; (3) the position sensor is visibly damaged or broken; or (4) the error persists after a full factory reset and all troubleshooting steps have been completed. If your printer is still under warranty, contact HP Support directly before attempting any disassembly, as opening the unit may void your coverage.

Frequently Asked Questions

What does error code 78 mean on an HP printer?
Error code 78 on an HP printer means the flatbed image scanner has failed to locate or return to its home (starting) position. This can be caused by a physical obstruction, a dirty or sticky scanner rail, a faulty home position sensor, or a firmware glitch.
Can I fix HP error code 78 myself without a technician?
Yes, in most cases you can fix error code 78 yourself. Start with a full power cycle, then clean the scanner rail with isopropyl alcohol. Most users resolve this error within 30 minutes using the steps in this guide. A technician is only needed if internal hardware like the scanner motor or position sensor is physically damaged.
Why does my HP printer keep showing error 78 after I restart it?
If error 78 keeps returning after a restart, the most likely causes are a dirty or partially obstructed scanner rail causing friction, a sticky scanner carriage that can't reach home position reliably, or an outdated firmware version with a calibration bug. Clean the rail thoroughly, apply a small amount of lubricant, and update your printer firmware to resolve recurring instances.
Will error code 78 prevent my HP printer from printing as well as scanning?
Yes. Because HP all-in-one printers perform a scanner calibration check during startup, error code 78 typically prevents the entire printer from functioning — including printing — until the scanner issue is resolved. Fixing the scanner carriage home position issue will restore full printer functionality.
Does HP error code 78 mean I need to replace the entire scanner?
Not necessarily. Error 78 most often results from a dirty rail, a minor obstruction, or a firmware issue — all of which are fixable without replacement parts. You would only need to replace the scanner home position sensor or scanner assembly if the sensor is confirmed to be physically defective or if the scanner motor has failed.

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