Short answer: If your Litter-Robot 4 says the drawer is full after you empty it, check the liner position first, then use Reset followed by Cycle so the machine can take a new reading. If the alert returns, follow Whisker’s sensor-cleaning and obstruction checks before considering calibration or replacement parts.
This guide covers Litter-Robot 4. A flashing blue light and an inaccurate percentage in the app are related observations, but write down which one you have. Instructions for Litter-Robot 3 and other automatic boxes are different.
Start with the symptom you can see
An owner in this Litter-Robot 4 discussion had emptied the drawer but still saw a full indication. Replies suggested checking the bag and sensors. That question is useful; it does not establish a failure rate or prove that every full alert has the same cause.
Before changing anything, take a photo of the light bar and a screenshot of the app. Record whether the robot completed a cycle after the drawer was emptied. Those details help distinguish a reading that has not been refreshed from an alert that returns after a completed cycle.
| What you observe | Where to start | What to record afterward |
|---|---|---|
| Full alert immediately after changing the bag | Check that the liner sits flat | Light pattern after Reset and Cycle |
| App percentage seems wrong, without a full alert | Follow the inaccurate-gauge guide | Percentage after a completed cycle |
| Full alert returns after a cycle | Follow sensor and obstruction checks | Whether the same alert returns |
| A different light pattern appears | Look up that exact code | Pattern, model and time it occurred |
1. Fit the bag before changing settings
Whisker’s inaccurate waste-drawer gauge guide says to install a new liner and press it against the drawer’s bottom and side walls. A stretched or raised bag can interfere with the reading. The company also says white bags work best; dark bags can produce less accurate readings, particularly in an empty drawer.
For this check, photograph how the liner sits before pushing the drawer back in. Avoid changing the liner type, litter and firmware all at once: if the alert disappears, you will want to know which change preceded it.
2. Let the robot measure again
The official flashing-blue troubleshooting guide explains that the drawer measurement happens during a Clean cycle. After fitting the liner, short-press Reset, then short-press Cycle. Watch for the robot to return Home with a solid blue light.
Use the result as your next decision point. If the alert has cleared, record what changed. If it returns, move to the next documented check instead of repeatedly pressing buttons or assuming that a different app percentage means the problem is solved.
3. Check the sensor area
Whisker’s laser-sensor cleaning instructions identify dust and fur around the bezel as possible sources of interference. The initial steps use a clean, dry cloth and a vacuum brush attachment. The full guide also covers carefully cleaning sensor surfaces with a clean, dry cotton swab.
Follow that illustrated sequence for your unit. Keep cats away during maintenance. Before removing the bonnet or globe to inspect deeper obstructions, turn the robot off and unplug it, as directed in the gauge troubleshooting guide. Do not improvise a sensor bypass.
4. Escalate with a useful record
If the problem persists, the flashing-blue guide continues through firmware, obstructions and DFI calibration. Open its current calibration instructions rather than copying a button combination from an unrelated model or an old comment.
Our suggested support note is short: “LR4; drawer emptied; liner fitted flat; Reset and Cycle completed; flashing blue returned.” Add the firmware version, photos and cleaning steps already completed. This gives support a reproducible sequence and helps avoid buying a board before the cause has been established.
Quick questions
Does pressing Reset prove the sensor is fixed? No. Check the result after the documented cycle. The useful observation is whether the robot completes it and the alert returns.
Should I replace the robot immediately? Complete the appropriate official troubleshooting path and contact support first. Our Litter-Robot 4 review explains its broader fit and maintenance considerations.
Is this the same as clumps sticking to the liner? No. Sticking clumps concern litter and cleaning behavior; this article concerns the drawer reading. Record both symptoms separately if both occur.
Sources
Manufacturer instructions and the selected owner question are linked beside the relevant points. Checked October 15, 2026.