Duplex not working - Laserjet 4300

[printer]

The configuration page lists "Duplex".
I have enabled duplex in configuration menu: "Duplex: Enabled"

If I print out the two-sided configuration page, this happens:

Page 1 is printing
Before the page is put out completely, it is going back into the duplexer for printing the second side
The page is completely within the duplexer
It seems not to work, the page comes out half
The duplexer takes the page again, the page is within the duplexer completely again
The page is outputted completely and put on the paper tray, but it is not printed on the second side
Page 2 is printing


Where could be the problem?

[printer]

I have seen the installation instructions on how to activate Duplex on Windows here in the forum. Great community! Printing duplex from windows works now. Two problems remain:


But the duplexer often has to insert the document twice to print it on the second side.
The printer squeaks while printing. I did not notice it before that. It may be because of the duplexer?

[redcow]

You might have a bad duplexer or a bad DC Controller

[woodss]

Or a bad duplexer solenoid.