How absolutely freaky that you should post this now.....I just sat down to post this..... Here's a my P140X story (totally relevant w/possible solution), and then you can decide for yourself what to do.
2002 Hyundai Accent
A few months back the Check Engine Light (CEL) came on with a code for P1402. The car was not and is not difficult to fill with gas. I got hold of the dealer service manual and was surprised to find very little information on the code. In fact there is no diagnostic flow chart for codes 1401, 1402, 1403, or 1404. It just lists a brief description of each code.... 1401-System Malf, 1402 Motor malf, 1403 Valve malf, and 1404 Heater malfunction (all for the DM-TL).
Having little choice for what to do, I ordered the part and replaced it. This solved the check engine light, and the computer passed all of it's self diagnostic modes. Everything has been fine for the past 2 months and about 1500 miles of driving.
Today, it came back on. This time with code 1401-- DM-TL System Malfunction. CRAP!!!
So, I called Hyundai Service Dept and begged for info on a diagnostic test for this code. Strangely, they were happy to consult me on this problem....as for a test.......SURPRISE-- THERE ISN'T ONE.
However, they did tell me that the DM-TL system is a common source of head banging (not the heavy metal kind) among their techs. They also suggested that I apply a small amount of silicone sealant to the electrical connector for the DM-TL, because they occasionaly get brand new units that leak air at the electrical connectors shortly after being installed and that this usually fixes the problem. Further that said that the harness itself isn't prone to failure (barring visible damage). The question stuck in my mind is that you'd think a leak in the pin area would cause a Evap Small Leak code..... but the tech didn't seem bothered by that....he didn't answer it either....any takers on that one?
The service guy told me (to my surprise) that if I applied the sealant and still experienced problems, he would see to it that the parts dept. exchanged my DM-TL for another new one.
If I were you, I'd remove the DM-TL, cover all the air ports and blow into one port (see if you can hear air rushing out at the pins or at the seam in the case)....even if it seems to be air-tight, I'd try doing the sealant thing first and if that is unsuccessfull, I'd replace the unit (still use sealant).
Because the tech I spoke to never suggested any other testing to perform, and because the book lists no other tests, I'm left to assume that if you get one of the DM-TL codes, the standard procedure for diagnosis is to stop diagnosing and just replace the unit with a new one. Anyway, I'll try to keep track of this thread and post back the results of my sealant test.
Also, I tested the Purge Control Valve, and made sure that the one way valve in the filler neck was working and that the gas cap was working and that there was no charcoal or air leaking from the container, and that there are no apparent leaks in the Evap System....not that the manual suggests it.
This is a very interesting "gremlin"...... does anyone else have any input on these codes.....and why isn't there a sticky somewhere, or a Hyundai tech on this forum to weigh in? That'd be very cool.