LJ M401dn with no physical jam under the cartridge

[BrickPilot]

Hi
I have one M401 which displays jam under cartridge. Sounds simple but
What happens is that the job completes and exits every single time with no other fault. Paper never stops in the path, rather after job completion it asks to check under cartridge. It is the same result whether a single page or 15 page print. There is no sign of late registration, or unusual engine sounds. The correct number of pages pick for the job and the job is printed correctly.

So far I have tried
Printing from MP or cassette and exiting face up or face down makes no difference
Print from host PC or PDF on USB stick makes no difference
Upgrade of firmware made no difference
Confirm page sizes match
Registration sensors seem to be ok with springs correctly returning them to home position. Firmware upgraded without issue

So what have I missed? I wait in hope that someone here can help identify the cause of this fault
TIA

[Elmtech]

Unfortunately the diagnostics on this unit sucks. No sensor test to speak of. Have you tried an engine test? At least you can possibly rule out the formatter. Also you can print an event log and post so we can see what jam the machine thinks it has. Instructions below.

Print the event log (touchscreen control panel)
1. Make sure the product is in the ready state.
2. From the Home screen on the product control panel, touch the Setup button.
3. Touch the left arrow button, and then quickly touch the Cancel button.
4. The product returns to the Ready state. touch the Setup button to reopen the menus.
5. Touch the 2ndary Service menu.
6. Touch the Service Reports menu.
7. Touch the Error Report item.

[mo0651]

Sounds like a fuser or exit sensor failure... How do you reset?? Power off/on??

[Printerdude]

Is the toner cartridge an OEM or remanufactured? Seen reman cause all many problems.

[BrickPilot]

Thanks Elmtech
Will visit today and see what we find with your suggestions
Yes I agree with your comments on the diagnostics. I look back into the likes LJIII service manual and then this service manual and the M401 more resembles an advanced users manual than a technical reference. "So do you think it was it written by an unusually gifted salesman with opposing thumbs?"

Thanks Field Supervisor
Fault clears with an open/close of toner door, returns to ready with no paper jam error ever. No paper is jammed in paper path. Yes this has me considering a sluggish rego on the fuser even though it looks to be working ok. Replacing the fuser is a $$ gamble. My bet was firmware but I was wrong, so I hope to somehow prove this first before getting a fuser in. I expected that if this sensor was intermittant then at some stage I should have had a page fail to exit, further it would be more inconsistant in stopping if the paper arm in the fuser was the cause. I do not see how rolling speed on the fuser could increase and there are no toner bonding issues or concertinering issues.

Thanks Printerdude
Yes cart was OEM, however I'll try and "borrow" one to eliminate this as a possible cause. I did look at the spring on cart cover flap and it seemed situation normal, however to find this to be the cause wouldn't surprise me.

[Printerdude]

Have you try printing the error log. Let's see what the error code and fault it is giving.

[Comingapart]

I've seen almost exactly the same problem be caused by low spring tension on the sensor in the registration unit. Not the one you can see from the process area, but the one with the lever between the registration and registration idler rollers. You have to remove the Tray 1 Assy and a few bits to see it.

Everything appeared to function properly, sensor was in place and tested ok, but for whatever reason, the spring didnt have enough tension on it and the armed dragged just slightly, enough to timeout and cause the message to appear after the machine outputted. Added a wrap to the spring and so far no call backs.....

[BrickPilot]

Ok some further results
The error log is reporting 13.00 only
Replaced the cartridge with another OEM out of the box without result

Thanks Comingapart, what you are saying makes good sense and will try this next.