Understanding Liftmaster Error 4

When your Liftmaster garage door opener displays Error 4 (four flashes or blinks), it's indicating that your safety sensors are either misaligned or obstructed. These sensors are crucial safety components that prevent the door from closing if there's something in its path.

What Causes Error 4?

Several factors can trigger Error 4:

  • Misaligned safety sensors
  • Physical obstructions in the door's path
  • Dirty or dusty sensor lenses
  • Loose sensor mounting brackets
  • Sunlight interference with sensors
  • Flickering green LED on receiving sensor

How to Fix Error 4

Step 1: Check for Obstructions

First, ensure there's nothing blocking the sensors:

  1. Clear any objects from the door's path
  2. Remove debris near the sensors
  3. Check for cobwebs or insect nests
  4. Ensure no stored items are near the sensors

Step 2: Clean the Sensors

Maintain clear sensor lenses:

  1. Use a clean, soft cloth
  2. Gently wipe both sensor lenses
  3. Remove any dust or dirt buildup
  4. Avoid using harsh cleaning chemicals

Step 3: Align the Sensors

Proper alignment is crucial:

  1. Locate both sending and receiving sensors
  2. Check that brackets are tight and level
  3. Adjust sensors until both LEDs are solid (not flickering)
  4. Ensure sensors are at the same height (within 6 inches of the floor)

⚠️ Important Safety Note

Safety sensors are a critical safety feature that protects people and property from injury or damage. Never attempt to bypass these sensors, and ensure they're working properly before operating your garage door.

Understanding Sensor Lights

Your sensors use LED lights to indicate their status:

  • Green light (receiving sensor): Should be steady when aligned
  • Amber light (sending sensor): Should always be on when powered
  • Flickering green light: Indicates misalignment or obstruction
  • No lights: Could indicate power or connection issues

Prevention Tips

To prevent Error 4 from recurring:

  • Keep the sensor area clean and clear
  • Regularly check sensor alignment
  • Secure loose mounting brackets promptly
  • Avoid storing items near sensors
  • Consider installing sensor shields in direct sunlight

When to Call a Professional

Contact a professional if:

  • Sensors won't stay aligned
  • LED lights aren't functioning properly
  • Error persists after all troubleshooting steps
  • Physical damage to sensors or brackets is visible