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SwiftRacer Roomba Diagnostics Articles


Roomba Diagnostic Mode

Ver 2005.03.15 By George F McQuary,

For information purposes only. No guarantee of accuracy. Not an employee of iRobot, merely a customer. Not responsible for warranty violation, injury, damages.

To proceed, you are doing so at your own risk; and, agree to the above disclaimer statement.

Please don't ask me to fix your roomba. :-)

First, if you've got battery problems the diagnostic mode won't help you. The solution to that is to make sure the unit is fully charged. If your battery isn't able to hold a charge then your battery is old and needs to be replaced. After that the most common problem is the unit being dirty and having fuzz or hair trapped somewhere it shouldn't be. Try cleaning it --compressed air works great! Assuming you’ve already cleaned your Roomba and are still seeing problems, here’s how to access the Diagnostic Mode.

Click here for the newer Roomba Discovery Diagnostic Mode

Entering Diagnostic Mode
First, remove your Roomba from all battery chargers. The safeties that prevent battery overheating are overridden in Diagnostic Mode so unplug the unit from the wall charger/remove it from its charging station.

Hold down the three S-M-L buttons all at once with power off. Press power briefly and wait ten seconds (this is so it won’t accidentally turn on and run off your tabletop) and it will give you a five note ascending scale. The power light will cycle in a cool rainbow mode showing 7 different colors by my count. (I have no idea how they do this with only three lights, but it appears each light has two brightness levels.)

You can now cycle between the ten diagnostic modes by using L to advance in the sequence, and S to return to the diagnostic mode before. The number of beeps will tell you which test you're in (count fast!) and it will actually count using a low note or a high note depending on if you ascended or descended in the test suite.

All the tests are quite useful except mode 10. The first four modes test the sensors and failure here is usually fuzz in the way of the optic sensor. (You also see this in mode 6). Modes 5-9 run each motor individually, so you can confirm that the motor is working properly.

Please note I'm using a Roomba Pro 2004 (blue). You may get slightly different results with other models --for instance, 2003 models combined diagnostic mode 8 and 9 together.

Mode 1 (1 beep) Bumpers and Wall Following Mode.

Pressing the Left side of the bumper turns the S light on.Pressing the Right side of the bumper turns the L light on.

The M light is turned on by the wall following IR in the middle of the right side of the bumper. Placing the roomba near a wall, using a book on edge, or even your hand to reflect the IR light on the right side will light the M light. This mode can be useful when adjusting the distance Roomba should use when cleaning edges with its edge brush.

S or L Failure: You’ve got some fuzz blocking the bumper's optical sensor holes and need to clean them out.
M failure: Clean the IR light and IR detector in the right side of the bumper.

Mode 2 (2 beeps) Left IR cliff edge sensors. RIGHT SIDE IS IGNORED

Put the roomba on a table. Slowly move the left side of the roomba off the edge while holding it in your hands. Hold it by the sides --holding it by the front bumper will block the IR sensors. The two IR sensors in the left side of the bumper will light when there is nothing beneath them.
Left bumper IR light: S light.
Left bumper IR in center/front: M light.

Failure: Clean out the IR sensors in the front bumper of any fuzz. If you think an IR light is blown, try using a digital camera to see the IR light --most cameras can see IR quite well.

Mode 3 (3 beeps). Right IR cliff edge sensors. LEFT SIDE IS IGNORED

Put the roomba on a table. Slowly move the right side of the roomba off the edge while holding it in your hands. Hold it by the sides --holding it by the front bumper will block the IR sensors.
Right bumper IR light is L light.
Right bumper IR in center/front: M light.
Left side is ignored.

Failure: Clean out the IR sensors of any fuzz.

Mode 4 (4 beeps). Extension of Wheels, Virtual Wall, and Remote

There's a lot packed into this mode. Usually the power light will turn from red to green once all sensors in that mode have been checked. In this mode, for most people, it will remain red all the time. This is not an indication of anything wrong with the unit itself. If you're really curious how to turn it green for mode 4: lift to extend the any of the three wheels until M lights, shine a Virtual Wall unit on the Roomba until S lights, then use the red button on the remote to light L. Who has the time to bother with all that? So normally you'll test your Roomba with the power light left red in mode 4, don't get obsessed with it.

M will light on full extension of any of these three: the front wheel, the left wheel, and/or the right wheel. By allowing these to extend one at a time, you can check all three sensors. (You may wish you had three hands to make this easier.)
S lights when a Virtual Wall is detected. You can easily check the different ranges on a Virtual Wall unit in this mode.
L lights when the Remote Control is detected. Only use the red button (the directional keypad, Max, and Spot on the remote are also harmless and all will cause L to light). Using L or S will change the diagnostic mode up to mode 5 or down to mode 3. Hitting P on the remote will turn the power off, bringing the diagnostic mode to an end ;-).

Failure: Clean the center wheel extender sensor, the left wheel extender sensor, and/or the right wheel extender sensor.
Change batteries in remote/Virtual Wall Unit. Clean the Virtual Wall Unit of any fuzz (tend to get in the hole). Check the range of the Virtual Wall Unit. Aim Remote correctly.


Mode 5 (5 beeps) is Move Straight Forward. Both wheels rotate straight forward ignoring all sensors and safeties.

Lay it on its back to inspect to check movement. Place on ground and let it roll forward to check straightness (the more off from straight, the more belt slippage from a worn belt you have on the side it curves to), but be very careful where you're aiming it as all safeties are off, and have someone ready to catch it before it runs into anything.

Allegedly the "S" light comes on if the Left wheel motor has a problem, the "L" light if there is a problem with the R wheel motor, and the "M" light if there is a condition with either. Most wheel failures seem to be too subtle to be caught by this diagnostic test though.

Failure: (check with mode 6 also)

If a wheel isn't moving, you've probably gotten a broken belt. If travels worse than a 45 degree from straight ahead on the floor (say in circles), you've probably got belt slippage from a worn belt. Check the article Roomba Belt Replacement. Within 45 degrees or less from straight ahead is considered acceptable belt wear by most owners and the Roomba has been found to clean just fine.

Mode 6 (6 beeps), Optical Rotor Test. Straight reverse both wheels plus optical sensor output for each wheel.

The S and L lights should flash as the beam separator for each wheel turns and is interrupted by the sensor blade. (This only happens in mode 6, not mode 5)

Failure: Usually if one side isn’t flashing or the other in addition to not spinning, it’s further confirmation that the wheel belt is broken (sometimes even blocking the sensor). If your wheel is spinning but the light is not flashing with the sensor, you’ve got some cleaning to do and it's probably just the optical fan sensor that has fuzz on it.

Mode 7: Brush motor in base.

"Small" light coming on shows an overcurrent to this motor. More common failure is the motor not turning at all.

Failure: The particular motor has hair wrapped around it and needs to be cleaned. At least one owner has had success spraying a commercial anti-static product ("Static Guard") on their Roomba to reduce hair wrapping.

Mode 8: Vacuum motor.

"Small" light coming on shows an overcurrent to this motor. More common failure is the motor not turning at all.

Mode 9: Side rotor brush.

"Small" light coming on shows an overcurrent to this motor. More common failure is the motor not turning at all.

Mode 10: Light check.

Lights S-M-L, but not Spot or Max (an oversight?) Power will be bright red. No known way to get power to turn green in this mode. Allegedly in the factory they use this mode to check the battery voltage sensor, but you'd need a variable voltage supply of the right wattage and all their other testing equipment as well to get it to work. For owners, it's a useful light check. ;-)

To exit Diagnostic Mode: press the power button again.

You can't enter diagnostic mode using the remote (it can't send three buttons being pressed at once), but once in diagnostic mode you can use the remote's S and L to change modes the same as the top keypad.

Some known differences for the 2003 Silver model:
Rainbow mode apparently not as fancy.
mode 4 does not test for remote.
Combines the vacuum and side brush tests into mode 8
No mode 9 for vacuum alone.

See also the articles: Roomba Diagnostic Songs, Roomba Belt Replacement, Roomba Problems.


[Other contributors: Michael Dwyer, Mike Tannenbaum]

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