When copier switch on, a appear L 4 and give a funny sound

You need to elaborate what "funny noise" your car is giving you. Does it try to tell you something ?
When does the "funny noise" appear? When you twist the starting key? If so, I guess it is the starter motor. The relay does not actuate and connect the gears on the starter motor to the gears on the flywheel.
If your battery is empty, you will hear just a short "knocking" from the relay on the starter motor.

Well I assume your wireless switch is on, so it does sound like a hardware problem with the switch. I know it sounds funny, but try jiggling it. Worst case would be to send it in and have them replace it.

You'll probably need to call a tech & have him Clean the sensor in the drum unit, chances are thats why you had faded copies in the 1st place,that sensor works with the tds sensor in the dv unit to add toner,good luck

enter the service mode by pressing 10871087 .there will be U000 then press 163 through keypad then press START button 4 times machine will restart .wola. check ur input voltage it is fluctuating

Try:

• The printer makes strange noises, or is noisy during printing
• How do I reduce noise in my printed photos?
• "The selected paper size is not supported by your printer..." appears after selecting the Paper Size in the printer driver.

Sounds funny but this model shows a jam when the exposure lite goes bad. Turn on the copier and watch the exposure lamp, should lite up and not flicker. Lamp is still available.

probably a defective toner cartridge, try another one.

check your timing belt positioning also inspect the top end with cover of possibly try an oil flush

I am getting the following message: "Error! Incorrect black cartridge installed". I don't understand why it's giving me that message when I have printed using the same cartridge. It's also making a funny sound, (like a hiccup sound). What could be the problem?

Funny stuff! Good to hear
Cheers