Hidden Roomba Diagnostic checks – Stuck Bumper Sensor

Roomba with stuck bumper sensor
The above video shows a roomba with a stuck front bumper sensor. As you can see, the robot keeps backing up and trying to turn away from
the phantom obstacle it thinks is in front of it. This particular sensor was triggering because lint had gotten into the optical beam path and was blocking light to the photodiode detector even when the bumper was not being hit. I was able to repair it by removing the bumper cover (unscrewing 4 screws) and vacuuming out the hole where the plastic pole from the bumper goes between the IR diode and photo-transistor.

I found the following website to be very useful when debugging the sensors on my Roomba to determine which of the front bump detectors were malfunctioning:

Update: Link dead, wayback machine version:


Summary: Hold the spot and clean buttons down. Push the power switch. Keep holding spot and clean buttons down while the robot gives five ascending beeps, and five descending beeps. Release spot/clean and you are in diagnostic mode.

Test zero: Flash all leds
Press clean to advance to the next test.
Test one: Bumper Sensors
Test-Four: WHEEL-DROP SWITCHES (3 ea) and WALL-SENSOR (1 ea)
Many other tests follow, but deal with motors, etc and can be dangerous if you let the robot run itself into something, because it will NOT automatically stop moving. Read the above linked page if you want to do any of the other tests.

11 thoughts on “Hidden Roomba Diagnostic checks – Stuck Bumper Sensor

  1. Wonderful! By just reading through the commentary, was enough to help me understand the theory of operation of a couple parts of my iRobot-700 series. Wasn’t cleaning as effectively as it did (7 years ago). Proceeded to disassemble and did cleaning/maintenance on the durt bin impeller motor. Thank you – back in operation, again!

  2. Hello, my Roomba 400 SE has also started to work in circles, first it goes backwards and then forwards and it doesn’t move forward, it just goes in circles.
    Thanks to you I found the diagnosis
    and disassembly
    page and I discovered that the fault is with the contact sensors (on the right) through test 1. I removed the external bumper and cleaned the sensor and it worked correctly again after 20 years old (bought it in 2004).
    Many thanks to all of you.

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