"Cleaned the sensors, but the red light persists?"

It is one of the most frustrating troubleshooting loops in the smart home world. Your robot vacuum stops, flashes a red light, and beeps an error code. You look up the manual (or Google it), and it tells you: "Cliff Sensor Error" or "Bumper Stuck."

So, you grab a cloth. You wipe the sensors. You use compressed air. You place it back on the floor, press start... and 3 seconds later, beep beep beep. It happens again.

Whether you own a Roomba, Eufy, Shark, or Coredy, if you have cleaned your sensors and the error persists, there is a 90% chance your sensors are perfectly fine. The real culprit is likely "Voltage Collapse" from an aging battery.

What is a "Phantom Sensor Error"?

A Phantom Sensor Error occurs when a robot vacuum's battery cannot supply enough power to keep the motherboard and sensors running simultaneously. The voltage drops, the sensors momentarily lose power, and the robot's brain interprets this signal loss as a physical sensor failure.

The Science: Voltage vs. Load

To understand why your robot is "lying" to you about the error, we need to look at how lithium-ion batteries behave as they age.

1. The "Surface Charge" Deception

An old or low-quality battery can often act like a mirage. When sitting on the charging dock, it can hold enough "pressure" (Voltage) to show a solid Green or Blue light. The robot thinks it is 100% charged.

2. The Collapse (The "3-Second" Rule)

The moment you press "Start," the robot engages its most power-hungry components: the vacuum suction motor, the main brush motor, and the wheel motors. This creates a massive, sudden demand for energy (Load).

A healthy battery handles this easily. However, a degraded battery has high Internal Resistance. It cannot release energy fast enough. Consequently, the voltage crashes instantly—often dropping from 14.4V to below 10V in a split second.

3. The Communication Breakdown

The robot's infrared sensors (Cliff and Bumper sensors) require a stable voltage to communicate with the motherboard. When the voltage collapses:

The power to the sensors flickers.
The motherboard stops receiving data from the Cliff Sensors.
The software logic defaults to a safety mode: "I can't see the floor! I must be hanging off a cliff!"
The robot stops and triggers the Cliff Sensor Error code (often 2 or 3 beeps).

Is Your Robot Affected? The Checklist

This issue is common across all brands, including iRobot Roomba (Error 6), Eufy RoboVac (4 beeps), and Coredy (3 beeps). Use this checklist to confirm if it's a battery issue:

✅ The Cleaning Test: Have you thoroughly cleaned the sensor windows with alcohol? If yes, and it still fails, suspect the battery.
✅ The Timing Test: Does the error happen almost immediately (0-10 seconds) after the robot tries to move? This is the classic signature of voltage collapse.
✅ The Age Factor: Is your robot or battery more than 18-24 months old? Lithium-ion batteries are consumables that naturally degrade after 2 years.
✅ The Third-Party Trap: Did you recently buy a cheap, unbranded replacement battery? Many generic batteries lack the high-discharge capability needed for vacuum motors, causing immediate errors.

Warning: Don't dismantle your robot yet! Many users tear apart their robots to replace expensive motherboard components or wheel modules, only to find the issue remains. Always rule out the power source first.

The Solution

If your robot passes the checklist above, the fix is simple: Replace the Battery.

Replacing the battery restores the "Amperage Muscle" needed to drive the motors without starving the sensors. In almost all cases, the "Sensor Error" will vanish instantly once a fresh, high-quality battery is installed.