Litter-Robot 4 pinch detect and bonnet errors: the real fix
- Yellow ping-pong light bar: the globe stops mid-cycle, retracts for a few seconds, pauses, then tries again — this is a pinch detect fault triggered during a cycle.
- Green and white alternating light bar: the same pinch detect fault, but triggered as the unit powers up, before any cycle starts.
- Yellow light bar flashing steadily (not ping-pong): a bonnet removed error — the unit won't cycle until the bonnet is confirmed closed. The Whisker app sends a push notification for both fault types.
- Check for debris first: open the waste drawer and look for anything that could be touching the pinch bars — this clears most faults.
- Run a test cycle: short-press Reset, then short-press Cycle, and see if the unit returns to a solid blue light bar.
- Clean the sensors directly: remove the bonnet and globe, clean both anti-pinch bars and the bonnet sensor, and check the carbon filter cover is fully seated.
- If a pinch bar won't click, or the bonnet still won't register closed: that's a hardware fault — you'll need a replacement base or bonnet, not a deeper clean.
Why pinch and bonnet errors happen
Litter-Robot 4 has two independent safety systems that will stop the globe from rotating the instant something looks wrong: anti-pinch bars that watch the waste chute, and a bonnet sensor that confirms the safety cover is actually on. Neither one is a "smart" sensor that can be fooled by software — they're simple mechanical switches, which means the fix is almost always mechanical too.
The anti-pinch bars
Two pinch bars sit inside the base, on either side of the dump port, and stay active at all times to catch anything — a paw, a tail, a clump of litter — before the globe closes on it. Litter dust and hardened clumps drift into this tight gap and settle over time. A carbon filter cover that has popped loose from the underside of the globe can also brush against a pinch bar mid-cycle and trigger a false stop.
The bonnet sensor
The bonnet covers the globe and guards the waste port while it rotates, so the unit checks that the bonnet is on before it will move at all. If the center tab at the top of the bonnet isn't fully seated in its pocket, if a latch didn't snap all the way, or if the sensor contacts have litter dust on them, the unit reads the bonnet as "off" even when it looks closed.
In most cases, the steps below clear either fault in under 15 minutes — no tools required.
How to fix it — step-by-step
Work through Part A if you're seeing a yellow ping-pong or green-and-white light bar. Work through Part B if you're seeing a steady yellow flashing light bar. Follow the steps in order.
Litter dust builds up in tight gaps fast
A can of compressed air clears the pinch bar housing in seconds, without taking anything apart.
If the issue persists: replacement options
Neither the anti-pinch bars nor the bonnet sensor are sold as standalone replacement parts — if cleaning and reseating everything doesn't clear the fault, the sensor has failed inside the base (pinch fault) or inside the bonnet (bonnet fault), and the fix is a full replacement of that part. If your unit is still covered by WhiskerCare® warranty, log in to your account and request the part free of charge through Whisker's support flow before buying anything.
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If you're not sure yet which part is at fault, the diagnostics below will help you narrow it down before you buy anything.
Advanced troubleshooting & diagnostics
A couple of edge cases don't fit the standard checklist above.
The drawer and sensors are clean, but the fault keeps coming back
Owners troubleshooting this exact fault have reported one pinch bar clicking normally while the other stays silent, even though both look and sit identically. If that's what you're hearing, the problem isn't debris — it's the switch itself, and no amount of cleaning will fix it. That's a base replacement, not a deeper clean.
The bonnet snaps shut but the unit still reads it as open
An audible latch click on both sides doesn't guarantee the center tab is seated — it's a separate connection point at the top of the bonnet, and it's easy to miss because the bonnet can look fully closed without it. Press down directly on the bonnet at the tab location; if it moves or clicks into place, that was the issue. If it's already seated and the fault persists, wipe the bonnet sensor contacts with a cotton swab and isopropyl alcohol, then check them for visible cracks — broken contacts mean a new bonnet.
For general Litter-Robot 4 cleaning intervals and odor control, see our full maintenance guide — Whisker doesn't publish a fixed cleaning schedule specifically for the pinch bars or bonnet sensor, so a quick wipe of both during every waste drawer change is the safest habit. If you're stuck after working through every step here, Whisker's own Troubleshooting Wizard and live support team can look at your specific unit; you're also welcome to describe exactly what you're seeing in the comments below.
Frequently asked questions
Can my cat still use the Litter-Robot while a pinch or bonnet error is active?
Yes — the litter box itself is still usable, since the fault only blocks the automatic clean cycle for safety reasons. The globe just won't rotate to clean itself until the fault clears, so you'll need to scoop by hand in the meantime.
Are pinch detect or bonnet errors a sign my Litter-Robot 4 is failing?
Not by themselves. Both are safety sensors doing exactly what they're designed to do, and most cases trace back to litter dust, a loose carbon filter cover, or a bonnet that isn't fully latched — not a failing motor or electronics. A sensor that won't click or register even after a full clean does point to a hardware fault in that specific part.
Where do I get official replacement parts for the base or bonnet?
Directly from Whisker. If your unit is under WhiskerCare® warranty, log in to your account, go to "My Robots," and request the part — it ships free with instructions. Out of warranty, you can buy the Litter-Robot 4 Base or Bonnet directly from litter-robot.com.
Conclusion
Pinch detect and bonnet errors look alarming on the light bar, but they're two of the most mechanically simple faults on the Litter-Robot 4 — and most of the time, a few minutes with compressed air and a cotton swab is all it takes. If you've worked through every step above and you're still stuck, tell us exactly what light bar you're seeing and what you've already tried in the comments below — we're glad to help you narrow it down.
Related Troubleshooting Guides
Litter-Robot 4: Only the Power Button Blinks Blue? (TB-LR4-010)
Litter-Robot 4 showing only a blinking blue Power button after an outage? Learn what Backup Battery Mode means and how to install or check the battery.
Litter-Robot 4® — TroubleshootingLitter-Robot 4 Smells Even After Deep Cleaning? Fix It (TB-LR4-014)
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The complete Litter-Robot 4 bulletin library
Every Litter-Robot 4 bulletin published on the site, in one place:
| Bulletin | Covers |
|---|---|
| TB-LR4-001 | Globe stuck? Solid or flashing red light on your Litter-Robot 4? Follow our expert… |
| TB-LR4-002 | Litter-Robot 4 flashing blue with an empty drawer? Clean the OmniSense laser sensors… |
| TB-LR4-003 | Litter-Robot 4 showing Motor Fault or Overloaded Globe? Fix blue/white and red/yellow… |
| TB-LR4-004 | Litter-Robot 4 won't connect to Wi-Fi or keeps going offline? Fix blinking yellow… |
| TB-LR4-005 | Litter-Robot 4 app showing wrong status, stuck offline, or not updating? Clear… |
| TB-LR4-006 | Is your Litter-Robot 4 malfunctioning or smelling? Our expert guide covers OmniSense… |
| TB-LR4-007 | Waste sticking to your Litter-Robot 4 globe liner after every cycle? Learn the free… |
| TB-LR4-008 | Litter-Robot 4 LED panel keeping you up at night? Learn how to turn off the Night… |
| TB-LR4-009 | Official Litter-Robot 4 liners cost $12–$55 plus shipping. See the exact waste drawer… |
| TB-LR4-010 | Litter-Robot 4 showing only a blinking blue Power button after an outage? Learn what… |
| TB-LR4-011 | A sourced reliability report on the Litter-Robot 4 beyond warranty — documented… |
| TB-LR4-013 | Small flies around your Litter-Robot? Moist waste-drawer residue attracts phorid… |
| TB-LR4-014 | Litter-Robot 4 still smells within hours of a full teardown clean? Worn seal strips,… |