13.12.00 duplex path, paper late jam. what should I do?

There are several thing which may cause unexpected jams in the duplex tray...,
1. first thing to do is eliminate all other possibilities by removing the netCard/Net connection Parralel connection so the machine is Stand Alone. make sure there is paper in the feed cassette 2 ( paper Tray)
press the TICK to enter menu
scroll down to diagnostic- press TICK
scroll down to paper path test - press Tick
scroll down to Source and select tray 2
scroll down to Duplex And select YES
( if the duplex option is not visible here then there is a connection/seating problem with the duplex tray)
Scroll down to copies and select 10
scroll up to print test page and press tick
the machine should now start duplexing 10 pages,
if you get the same error ( 1 page enters then jams)
it could be a dirty/snapped paper entry sensor,( looks like a little plastic match stick that protrudes into the feed path of the paper)
use a can of pressurised air to Blast any dust away from this arm and the surrounding area being careful to follow the Paper sensor Arm back to the sensor and blasting this as well-
Duplexer tray are cheaper than an engineer call out, if the fix above fails , your cheapest option may be a replacement Duplexer tray, available from most HP office equipment Stores as well as Belmonte Business Equipment.

>Remove back cover(duplex) check any paper object jammed? remove it.. >remove paper tray observe any paper objects visible? remove it>Check paper path sensor located at the path of carriage assembly.. observe for free play of sensor flag...

13.20.00 JAM INSIDE <LOCATION>

Paper has not moved past a certain paper
sensor. <LOCATION> can be one of the
following locations.

? TRAY 2
Remove the tray, and then check the
paper path for obstructions. Perform a
manual sensor test and observe the prefeed
sensor (PS102) status (B). Toggle
the sensor flag to determine if the status
changes.
? TOP COVER
Remove the print cartridge, and then
check the paper path for obstructions.
Verify that the top-of-page sensor
(PS103) and the media width sensors
(PS106 and PS108) are unblocked.
Perform a manual sensor test and
observe the status of these sensors.
Toggle the sensor flags to determine if
their status changes.
? REAR DOOR
Open or remove the rear face-up bin,
and then check the paper path on each
side of the fusing assembly for
obstructions. Remove the fuser, if
necessary. Perform a manual sensor
test and observe the fuser delivery
sensor (PS700) status (C). Toggle the
sensor flag to determine if the status
changes.
? DUPLEXER (only printers with duplex)
Remove the duplexer, and then check
the paper path for obstructions. If the
message persists, replace the duplexer.

Thank you contacting FixYa for your printer inquiry.
This error is associated with either a sheet of paper blocking the paper path or a partial piece of paper that blocks path or trips a sensor. The printer will usually throw up a error code 13.XX on the display and the XX is a number that will indicate where in the paper path this error most probably occurred. Just follow the steps for your error on the below chart.
This link will take you to the user guide which will be helpfull identifying components and providing guidelines for most of the helpful hints and things you will need to know about this printer.
http://bizsupport2.austin.hp.com/bc/docs/support/SupportManual/c00218691/c00218691.pdf
Locate your error on the matrix below and follow the steps. Comment back if you need more help. Thank you again for contacting FixYa.
TF
HP Laserjet Error Codes 0 - 19 Message on printer Display Panel What it means. What to do. 13.XX PAPER JAM [LOCATION] Media is jammed at the specified location (and possibly at other locations). If the message persists after all jams have been cleared, a sensor or sensor lever might be stuck or broken. For all jam messages, do the following: 1. Remove jammed print media from the specified location. Check the entire paper path for other pieces of media in the path. 2. Open and close the top cover to clear the message. 3. Check sensors and flags in the paper path for proper operation. 3.0 PAPER JAM [LOCATION] A non-specific paper jam occurred. 1. Remove jammed media from the specified location. 2. Verify the paper tray is fully closed. 3. Inspect and/or replace the feed and separation rollers. 4. Ensure there is no obstruction in the path, such as a torn piece of paper. 5. Open and close the top cover to clear the message. 6. Check sensors and flags for proper operation. 13.1 PAPER JAM OPEN INPUT TRAYS Paper-delay jam at paperfeed area. 1. Ensure that paper trays are loaded and adjusted properly so media can feed from the tray. It might be necessary to reduce the stack height of media in the tray. 2. Check the input area for obstructions such as media in the path. Also check to see if the registration assembly damaged or unseated. 3. Replace any defective sensors or flags. 4. Verify the media meets the specifications. 5. Check the pickup feed and separation rollers for unusual wear. Replace as needed. 6. Rotate the media in the input tray by 180° and/or turn it over On NX engines this is most likely the fuser flag or the ACPM. The ACPM has a photosensor hard-wired to the back of it. 13.10 PAPER JAM CHECK DUPLEXER Jam at duplexer. 1. Check the duplexer and the rear area of the printer for obstructions or damage. 2. Check the duplexer for proper operation. Replace the duplexer if a sensor is defective. On a 5si, 8000, or 8100 series laserjet a Duplex Jam can be caused by a tray 2 and 3 feed assembly failure. 13.14 For Laserjet 5si. This error is caused by a defective paper control PCA Replace paper control PCA. 13.2 PAPER JAM OPEN INPUT TRAYS Paper-stopped jam at paper-feed area. 1. Check the input area for obstructions such as paper in the path. Also check to see if the registration assembly is damaged or if the transfer roller is out of place. 2. Replace any defective sensors or flags. 3. Ensure the media does not exceed the maximum length. 4. If multiple sheets are feeding, it might be necessary to fan the media and reduce the stack height. Also, replace separation pad. 5. Verify that the fuser is properly installed. On NX engines this is an input jam. 13.20 PAPER JAM CHECK REAR DOOR Media stopped in the paper path during power on or when the top door was closed. 1. Remove all media in the paper path, and then open and close the top cover. 2. If the message persists after all media is removed: Check if media is jammed in the prefeed area. Replace any defective sensors or flags 13.21 DOOR OPEN JAM The top cover was open while printing. 1. Clear the jam and close the top door. 2. If the message persists, check the top door switch for proper operation. 13.5 PAPER JAM CHECK REAR DOOR Paper-delay jam at fuser. 1. Check the transfer roller and small media belt to ensure they are operating and can feed print media. 2. Check the paper path for obstructions at the transfer roller, toner cartridge, paper feed assembly, and fuser. 3. Replace any defective sensors or flags. 4. Turn the media stack over and/ or rotate it by 180° in the input tray. If still persists - replace fuser, then DC controller. 13.6 PAPER JAM CHECK REAR DOOR Paper-stopped jam at fuser. 1. Check the paper path for obstructions at the fuser and output/delivery area. 3. Replace any defective sensors or flags. 13.99 PAPER JAM [LOCATION] A non-specific paper jam occurred. 1. Remove jammed media from the specified location. 2. Verify the paper tray is fully closed. 3. Inspect and/or replace the feed and separation rollers. 4. Ensure there is no obstruction in the path, such as a torn piece of paper. 5. Open and close the top cover to clear the message. 6. Check sensors and flags for proper operation

this will be an issue with the duplex rollers check where it is jamming is it in the duplex unit if yes then check the duplex rollers for wear worn rollers will cause scews also check there is no torn pieces of paper stuck in the guides of the duplex
a good thing to do is to get a thin piece of card stock slide it into the duplex manually and frred it where the paper path goes on the duplex from beginning to end and it will push out any thing in the path

paper jam on hp laserjet

13.10.00 jam inside lower left door or 13.10.00 jam inside duplexer Description A media jam has occurred in the duplexer area of the printer. Action

1. Check for stuck media in the paper path around the fuser and duplexer area. (See the paper jam locations in the printer section for further assistance).
2. Make sure hat the lower left door closes properly.
3. If this message persists, contact an HP-authorized service or support provider. Click here to go to "Handling persistent messages?? above.

my experience says jamming in duplex area using card stock. this may occur if default is duplexing. set default to single side and / or try same job using plain a4 80gm2

Pull up the document feeder door to open and make sure there are no obstructions in the feeder.

Can you save that one document as a pdf and print it?