Black ink? The printer does not print in black. The black cart. is full. Icleande the jets several times to no avail. Please help.

Unfortunately, the printer does not actually measure the ink in the carts, but measures how many droplets called for. The carts may actually be full, but the printer now thinks they're empty. Most likely the black ink needs to be "charged" because you've cleaned out the pipe. I don't know what to do to charge it, and you'll likely need new carts.

All ink jet printers act this way. All carts must have ink in them.

Ink Carts do act finicky at times. Especially Canon carts.
In many cases, the ink carts have a small fuse built into the back of the cartridge that opens up if the cart has been removed for any reason. Replacement Carts come with the fused portion reset, thus when you insert it into the printer, it works great. If the cart is FULL, it still may not be observed as full or new by the Printer itself. Best way is to use a new cart, not necessarily a Canon Brand. Use an inexpensive company like
https://www.carrotink.com/canon-pgi-5-cli-8-combo-10-pack-ink.html

When opening the print dialog, there is a button for performing maintenance. On the maintenance menu, there is a button for clearing the print jets. That did the trick.

two diffrent errors:

1. near empty. I guess your cart is at full level.: Take cart out. unplug dcp from power. leave scanner open. replug to power. machine will come up and demanding cart. insert cart. close cover. answer display if its changed!

2. press menu then start bk-copy then four times arrow up. machine will be in maintenance mode. press by help of arrow-up and set: 7 (set) 6 (set) 3 (set) start bk-copy. machine will do a power purge cleaning. when finished press 9 (set) 9 to leave maintenance mode. run a test print and set date/time again!

Did you make sure that the cart was placed well and the plastic hook secures the cart on top?

If you have used Easy Jet carts, you can stop here and give the whole machine a push to the bin!
Easy Jet carts and some other generic ink carts clogg the fine filter in front of the nozzles which cant be cleaned anymore.

The ph as a spare part is more costly than a new mfc 240c at a price discount!

But you can try this at least:
Use a new original brother carts (BK/C/Y/M). place carts and secure them! (this procedure will consume some ink!)
press menu then start bk copy then fourtimes arrow-up button. machine will be in maintenance mode. press 7 then 6 then 4 then start bk copy. machine will refresh ink in tubes and ph
and will do some cleaning cycles. when finished press 7 then 6 then 3 then start bk copy to run a special power purge.
When finished press 9 then 9. After machine is back in normal state run a test print.
If you still cant see any bk the ph cant be fixed anymore.

This could be to several reasons:
1#  The black cart contains blue ink-> Change to a brand new cart.

2# The cart assy has a bottom that is a foil. Sometimes this foil leaks.
Ink will mingle: You need a new cart assy.

Run the cleaning cycle twice after inserting a brand new bk ink cart and print out a test print. If you still see blue instead of bk the assy is leaking.
BTW the bk is darker than blue (or better cyan). You must see bk! So it seems to be the prob with the right ink....

Unplug machinepowercord. Open printer and take all carts out. Plug in power. Machine demands carts. Put new one in: Replace with original ink carts!. When asked push 1 (yes New cart). If you have used thirdparty carts, there could be a prob due to construticon or ink quality. In case there is no bk after 3x cleaning cycles anymore, the head is clogged: This happens because the filter in front of the nozzels is clogged by pigmented ink. DO USE ONLY DYE INK for all types of brother inkjet machines!!!

Did you use third party ink? If the ink is pigmented the filter in front of the printnozzels is clogged and cant be cleaned any more. What you can try is to buy a brand new original brother ink cart and do the cleaning 3 times. After that do a testsheet printing. In case its OK, your lucky and it was a problem of the cart. If you cant see any blocks (with the original ink used!!!) the printhead is crashed and has to be replaced (BTW: Its cheaper to buy a new mfc)! Do use only dye ink for brother printers!!!

Cleaning cycles use ink. So it's no wonder it got worse, the ink level went down. Are you 100% sure that the black cart is full? they can give a wrong reading on occasion. what makes you think its full? Could be also that you need to replace the head- the part the cart fits into. generally they don't last more than 18 months.] Another possibility is that the black is indeed full, but dry. Put a wet sponge to the nozzle, see if it soaks up a decent amount of ink. Good luck