trying to scan from my phone with the hp smart app and it just won't find my 4155e printer.

Diagnosis

The inability of the HP Smart app to locate the DeskJet 4155e usually stems from a breakdown in the "handshake" between the mobile device and the printer's wireless radio. This most commonly occurs because of Network Segmentation. Many modern routers broadcast dual-band signals (2.4GHz and 5GHz) under the same SSID. While your phone may be utilizing the faster 5GHz band, the DeskJet 4155e is limited to 2.4GHz. If your router does not support "Band Steering" or has a strict firewall between bands, the app will fail to "see" the printer even though both appear connected to the same network name.

Another frequent cause is the "Setup Mode" timeout. The 4155e enters a specific discovery mode for 2 minutes after being powered on or reset. If the app is launched after this window expires, the printer stops broadcasting its discovery beacon, making it invisible to the HP Smart app. Additionally, if you have a "Guest" network enabled on your router, these networks are designed to isolate devices from one another for security, effectively blocking the communication path required for scanning.

How to Fix It

Follow these exact steps to force a reconnection and clear the communication bridge:

1. Reset Network Settings: On the printer control panel, press and hold the Wireless button and the Cancel button (the X) simultaneously for exactly 5 seconds. The power button will flash, indicating the network settings have been cleared and the printer is now in "Setup Mode."
2. Force Phone Connection: On your smartphone, go to Settings > Wi-Fi. Look for a network named "HP-Setup-4155-DeskJet." Connect to this network directly. If prompted for a password, leave it blank or check the printer's information page.
3. Refresh the App: Completely force-close the HP Smart app (swipe it away from your recent apps list). Re-open the app and select "Add Printer" or the plus (+) icon.
4. Assign Network: The app should now detect the 4155e in setup mode. Select the printer, then choose your home Wi-Fi network from the list and enter your password. Wait for the wireless light on the printer to stop blinking and remain solid blue.
5. Verify Scan Permissions: When the app asks for permission to access "Local Network" (iOS) or "Location" (Android), select "Allow While Using App." Without these specific permissions, the app cannot scan the IP range of your router to find the hardware.

If That Didn't Work

• Disable 5GHz Temporarily: Log into your router's admin panel (usually 192.168.1.1) and temporarily disable the 5GHz band. This forces your phone onto the 2.4GHz band, ensuring it is on the exact same frequency as the printer. Once the scan works, you can re-enable 5GHz.
• Clear the HP Smart Cache: On Android, go to Settings > Apps > HP Smart > Storage > Clear Cache and Clear Data. On iOS, delete the app entirely and reinstall it from the App Store to clear corrupted cached network profiles.
• Check IP Conflict: Print a Network Configuration Page by pressing the Information (i) button. If the IP address starts with 169.254, the printer is not actually connected to the router and is using an APIPA address. Perform a hard power reset by unplugging the power cord from the back of the printer for 30 seconds while the printer is on.
• Disable VPN: If you have a VPN (like NordVPN or ExpressVPN) active on your phone, the app will be unable to see local network devices. Turn off the VPN entirely before attempting to link the printer.

Heads Up

• Avoid Guest Networks: Never connect your printer to a "Guest" Wi-Fi network; these are designed to prevent the exact type of device-to-device communication required for scanning.
• Static IP Assignment: To prevent this from happening again, use your router settings to assign a "Static IP" or "DHCP Reservation" to the printer's MAC address. This prevents the printer from changing addresses and "disappearing" from the app.
• Update Firmware: Once connected, check the "Printer Settings" in the HP Smart app and run any available firmware updates. HP frequently releases patches to improve wireless stability for the 4100 series.
• Power Cycle Sequence: If the connection drops, always restart in this order: Modem/Router first, then the Printer, then the Phone.