Autofocus is not engaged on the lens
Before taking anything apart, check to make sure autofocus is engaged on the lens. The autofocus mechanism is activated by flipping the switch on the side of the lens to the “AF” position . If it’s still not working then check to see if AF is engaged in the camera (refer to the autofocus section of the user’s manual) . If you are still having problems then it’s most likely a bad focusing screen.
Bad focusing screen
The focusing screen may be damaged or missing, not allowing the camera to find focus. If you take the lens of the camera off there should be a focusing screen above the mirror. If it is there and is not working it may need to be replaced.
Lens autofocus non functional
The autofocus motor may not be functioning inside the lens. Try a secondary lens and if the camera focuses then the lens needs to be fixed or replaced. Make sure that the mechanism hasn’t been stripped. You can check this by engaging the AF switch on the side of the lens and gently turning the focus ring. If the mechanism is intact, you should feel a slight resistance offered by the motor followed by a very low, revving sound. If this is not the case, and the ring turns freely with AF engaged, refer to the user’s manual for your specific lens to make sure this is normal (it usually is for Canon L-series lenses, which enable full-time manual focusing while in AF mode). Otherwise, the servo assembly will have to be replaced.
Broken power button
The power button may not be functioning not allowing the camera to turn on. Take out the battery and try to charge it. If the battery is fully charged and the camera won’t turn on then you may need to replace the power button or have a bad Logic Board.
Display screen is off
Check to see if the screen is on before taking anything apart. If the display screen is off, press the display button to turn on the display. If it does not turn on make sure your camera is on and functional. If not then you may need to replace the battery or you may have a bad Logic Board.
Bad logic board
The logic board may not be functioning, not allowing the camera to turn on. If all else failed you have a bad Logic Board.
Can’t see image
You are unable to see anything on the camera’s LCD display. Make sure you do not have the screen saving mode enabled (check the user’s manual). Also, try pressing the quick menu button on the back of the camera. If this does not engage the screen, there may be a software problem.
No battery or power source
Check to make sure that a genuine Canon battery is installed and fully charged. If there is no battery then install one. If the battery is not charged then charge it. Try to turn on your camera, if it doesn’t work you may need to replace your battery. Often, aftermarket (non-Canon) batteries can cause damage to the camera so try to avoid using these.
Screen is cracked
The camera’s screen may be damaged or cracked resulting in the screen not functioning. Check the integrity of your screen by turning the camera on. It may be possible to continue using the camera, since this model has a thick layer of plastic overlaying the actual screen. What you may be seeing is a crack in that outer plastic layer and not the LCD screen. If this is the case, you should be able to see the data being presented by LCD fairly clearly, depending on the severity of the crack in the plastic.
Display is turned off
Check to see if the screen is on before taking anything apart. If the display screen is off, press the display button to turn on the display. If it does not turn on make sure your camera is on and functional. If not, then you may need to replace the battery or you may have a bad Logic Board.
Error 20 - Mechanical Malfunction
When turning on the camera you receive the "Err20" message.
Shutter may have a problem
The shutter may be stuck, creating an error message. The shutter release button is built into the top of the body of the camera (check the button layout in your user manual). The shutter release button is often referred to as the focus/shutter button, since it has two steps (pressing halfway down focuses, pressing all the way releases the shutter and takes the photo). If the camera doesn’t react when you hit the shutter, then it may very well be obstructed. Remove the lens, gently move the mirror out of the way and check to make sure nothing has gotten jammed in the shutter curtain (make sure you do not expose the sensor to dust, oil, or fingerprints).
Mirror may have a problem
The mirror may not be working correctly resulting in a error. Remove the lens and check to make sure that the mirror is not being obstructed by foreign particles. If this does not appear to be the case, apply very little force to the mirror using your fingers (try to do this with latex gloves on, so you don’t get fingerprints on the mirror). If the mirror does not freely move up and down, then the actuating mechanism for the mirror may be jammed. If the mirror does move, then there may be a firmware issue.
Aperture may have a problem
The aperture diaphragm in the lens may be stuck. To free it, carefully open the lens and manually move the aperture. If it resists, do not apply additional force. Try to free up any obstructions by gently blowing air (in a dust free environment) into the mechanism.
Error 01 - Communications between the camera and lens is faulty
When turning on the camera you receive the "Err01" message.
The contacts on either the lens or camera body may have debris blocking communication. Try to clean the lens or camera body. If the problem persists, try a secondary lens. You may also need to replace the lens.
Fault in the ribbon cable
There may be a problem with the ribbon cable carrying the lens information. Open the camera and check to see if the ribbon cable is intact. If it is, clean the ribbon cable. If it is not you may need to replace the cable.