New member so I hope I am posting in the correct section. Our 2004 HL757-7 has a gear selection problem. When using any gear the unit will shift into double neutral intermittently. Issue is worse in cold weather. To get it working again, we must shift back to neutral, rev engine a few times, then select gear and unit will work again for 5 or 10 minutes. Unit sets code 12, logical error.... I have disassembled selector switch and although there were a few aluminum flakes, the switch seems ok and seems to test ok with ohmmeter. I have tried replacing the relay, but don't know how to troubleshoot further. Unit has 5000 hours.
Is it possible the trans filter could clog or gum up and cause these symptoms? We will check that out.
Hi rustfarmer, the issue is definitely around gear selector. TCU is throwing code 12 with overlap of F, N or R signal. Check (again) switch itself, connectors, cable harness from switch to TCU. Has nothing to do with trans filter or trans hardware. good luck
Thank you so much for your response. The shop manual I have is poorly organized and hard to read. It would really help if you could tell me where the TCU is located.
On the Hyundai it is usually behind the Seat. Some compartment with bolts or clamps to Open.
Thank you. That really helps.
Hi, did you solved it, have same problem?