Litter-Robot 4 pinch detect and bonnet errors: the real fix
- 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.
- 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.
Your cat may have no usable box right now. Cats that can’t get in will hold it or find another spot in the house — put a spare tray down before you start, so nothing depends on how fast this goes.
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.
A pinch-detect halt looks like a serious malfunction if you don't already know what it means — exactly the position a sitter is in when you're not home. A one-page reference tells them in seconds whether to fix it or just wait for you.
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Bonus resource for LR4 owners
Leaving your LR4 with a sitter?
A printable quick-reference sheet that tells them exactly what's normal, what to fix in under a minute, and when to actually call you — no app, no account needed.
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.
Don't confuse this with a red ping-pong light bar
Whisker documents a fourth, easily-confused light state: a red ping-pong light bar, not yellow. This is a separate fault — "Motion in Drawer" — triggered by the SafeCat motion sensor detecting movement in the waste drawer itself (commonly from removing and reinserting the drawer in quick succession, or from something shifting inside it), rather than the anti-pinch bars. The globe cycles to the Dump position to let the object clear, then resets. The fix overlaps with the steps above — check for foreign objects in the drawer, inspect and clean the anti-pinch and cat-presence sensors, and reassemble — but if a red ping-pong persists after that, it points to the cat-presence sensor or base rather than the pinch bars specifically.
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.
What's the difference between a yellow and a red ping-pong light bar?
The color tells you which sensor triggered the stop. Yellow ping-pong is the pinch detect fault covered in this guide — the anti-pinch bars near the dump port. Red ping-pong is a separate fault called "Motion in Drawer," triggered by the SafeCat motion sensor when it detects movement in the waste drawer itself, often from removing and reinserting the drawer quickly. Both use the same retract-pause-retry pattern, but the fix starts in different places.
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.
Still not fixed? Here’s what to do next.
Some faults are genuinely hardware, and no amount of cleaning or resetting will clear them. If you’ve worked through everything above and it’s still doing it, stop here rather than taking the unit further apart.
- Go to Whisker (Litter-Robot) directly. If the unit is still under warranty, let them replace the part rather than paying for it yourself — contact Whisker (Litter-Robot) support.
- Tell us what didn’t work. We rewrite bulletins when readers show us a case they don’t cover — compliance@pet-infrastructure.com. Tell us the model, what the lights are doing, and which steps you already tried.
- Ask other owners. r/litterrobot is active and full of people who have had the exact same fault on the exact same model. Search the sub before posting — the answer is often already there.
When to stop and call the manufacturer: if the fix needs the base opened, the motor or control board touched, or any tool beyond a screwdriver — stop. On a unit in this price range, opening it yourself usually voids the warranty, and a warranty repair costs nothing.
Did this actually fix it? 🐾
The complete Litter-Robot 4 bulletin library
Every Litter-Robot 4 bulletin published on the site, in one place:
| Bulletin | Covers |
|---|---|
| TB-LR4-001 | Solid red, flashing red, red with yellow, red with blue: here is what each… |
| TB-LR4-002 | Litter-Robot 4 flashing blue with an empty drawer? Clean the OmniSense laser sensors… |
| TB-LR4-003 | Blue and white lights, or 'Overloaded Globe' in the app? It's usually litter packed in… |
| 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 | Litter-Robot 4 malfunctioning, cycling stuck, or smelling despite regular cleaning?… |
| TB-LR4-007 | Liner not dropping, or waste sticking after each cycle? Usually the liner weight has… |
| 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,… |
| TB-LR4-015 | Litter-Robot 4 dumping clean, unused litter into the waste drawer? Learn the three… |
| TB-LR4-016 | Litter-Robot 4 carbon filter needs replacing? Here's exactly where it sits, how to… |
| TB-LR4-017 | Litter-Robot 4 panel flashing blue and purple, or just unboxed the LitterHopper?… |
| TB-LR4-018 | The complete Litter-Robot 4 maintenance guide: daily cleaning routine, odor fixes,… |
| TB-LR4-019 | Litter-Robot 4 acting up? Match your exact light, connectivity, or odor issue to the… |
| TB-LR4-020 | Cleaning and resetting didn't clear the fault? Compare the Litter-Robot 4 motor… |
| TB-LR4-021 | Three Litter-Robot 4 laser boards sell for $50 under different SKUs. Which one matches… |
| TB-LR4-022 | A new Litter-Robot 4 motor that faults again within days points somewhere else. What… |
| TB-LR4-023 | A carbon filter only treats the air that passes through it. How to size and place a… |
| TB-LR4-024 | Litter-Robot 4 not cycling after your cat uses it? Match the light bar color to the… |
| TB-LR4-025 | Position fault on your Litter-Robot? What it means on the LR3, LR4, LR5 and EVO, how… |
Written by Alberto Guardia
I’m a physician working in medical informatics, and I run Pet Infrastructure on my own — no team, no manufacturer sponsorship, no paid placements. I share my home with Wolfgang, a 13-year-old Chartreux with firm opinions about litter and none whatsoever about firmware.
How this page was put together. Every light code, button sequence and timing here is traced back to Whisker (Litter-Robot)’s own documentation, to official support articles, or to several owner reports that agree with each other — and the guide tells you which. Where something genuinely isn’t documented anywhere, I say so instead of filling the gap.
How I check every guide → · Last updated August 2026