Why does my printer print papers with lines and faded

Are you using OEM or 3rd party toner? The HP toner for these is the all-in-one type, so if you're using 3rd party toner on its 2nd or 3rd refill, issues like this can/will come up. Most 3rd party toners are only refilled and remanufactured once, but some of the less credible brands use 2nd or 3rd cycle toners for their reman toner. If the toner is OEM, then this probably isn't a problem. If the toner is OEM, shake it 20-30 times by rocking it back and forth, redistributing the toner. If you need to replace the toner, I'd buy all 4 toners and only replace the ones in immediate need. See here for a good 3rd party toner.

If, for some reason, the shaking procedure does not help, try to look for any spilled toner in the machine, especially above the transfer belt where the lasers live (look for 4 slits when you have the toner tray removed; it may be hard to find on these if you don't know what to look for the first time) and see if you see any stray toner. If you do, you may have to take the printer apart to get to the laser unless it's minor, and you can get it cleared with canned air. If you can take the toner tray out, that will give you much better access. If you can find reman toner for it, I wouldn't be opposed to tying it but remember: Known brands only to avoid 2nd/3rd generation remanufacturing issues.

If neither fixes it, you want to run a swatch test like this to see which toner(s) are causing the issue. Usually, when problems like this come up, they're isolated to one or two toners and aren't the entire set, but they throw off the machine and affect the entire print run. Here is an example of how it works to isolate bad toners (all 4 toners are low, have drum defects or minor toner shed):

I also have 4 sheets I've made for troubleshooting toner carts like this (CMYK hex coded to avoid the RGB processing skew issue, and exported in CMYK/8 to PDF):

K TestC TestM TestY Test