Verify that the Sensor Bar is firmly plugged into the rear of the console. As a precautionary measure if it is inserted, remove the plug from the rear of the console, firmly re-insert the Sensor Bar then retest.
Verify the Sensor Bar location and ensure it is placed either above or below the television, with the center of the Sensor Bar being level with the centre of the screen. Try reversing its current location e.g. If it is resting below the screen then move the Sensor Bar so it rests above the display screen.
Check that the Sensor Bar cable is free from any splits, breaks or frays. If any of these are detected at any point in the length of the cable the Sensor Bar will need to be replaced.
The sensor bar can be affected by bright lights or a reflective surface e.g. mirrors or large windows. Verify if any of the described are in the room and try to minimise their presence, e.g. close the blinds or curtains, switch off any lighting or cover/move the reflective surface. Relocating the console to another room may also correct the issue.
Verify the health of the Wii Sensor Bar. This is done by viewing the infrared lights emitted by the device which interact with the IR sensor on the Wii Remote. These lights are not visible to the naked eye; however they can be detected by using a digital photographic device which utilises an LCD screen (such as a digital camera or mobile phone camera).
If possible look through the image viewer of one of these devices at the two opposing ends of the sensor bar. When performing this generally you should expect to see an equal number of Infra Red lights on both the right hand and left hand side of the sensor bar. If this is not the case the Wii Sensor Bar may require replacement.