Howdy,

About a month ago my 2014 Multivan (DQ500 DSG) started occasionally dropping into Neutral while driving (revs climb and gear indicator on dash flashed on and off) and then it resumed driving after a few seconds. (Sometimes it would flash the spanner icon and I would roll to a stop and wait 5-20 minutes and it would come good).

As time went on, the issues became more frequent, and continued to be intermittent with seemingly no external factor influencing when it would trigger.

After a lot of diagnosis, it appears that somehow the "Always On Power (Terminal 30)" is intermittently dropping, we could watch it live and see voltage at 13volts, and then suddenly it would be sitting at 3v, climb to 4v, slowly move up to 6, and sit there for some time, with seemingly no external factors influencing this (although it could possibly relate to the car getting warmer/cooler over time).

There were times where I could drive for 45 minutes on the highway with no issues, then there are times from cold where you could drive for 2 minutes and the problem appeared.

Ultimately our understanding is concluding that it is either some sort of wiring issue, or possibly internal issue in the TCM (Transmission Control Module).

We replaced all the fuses, and also one of the relays under the battery, however no changes were observed.
My mechanic has wired up a bypass to have voltage go directly to the pin on the Mechatronics unit from the battery, and the issue still seems to persist.
We have also replaced the internal contactor PCB, as well as all the solenoids/valves inside, with no change.

The strange thing is that this data is being read out of the TCM - the TCM itself is telling us the voltage from the Always On Power is wandering around at lower voltages (3-6v) and then randomly normal at 13-14v.
The Switched-Ingition-On (Terminal15) voltage is reading a constant 14v in line with the battery.

All other modules in the car are working and no voltage issues reported. The battery is about 4 months old and appears normal, engine cranking speed is excellent etc. so I don't believe there is any sort of general power issue in the vehicle, just something specific to the DSG.

As far as we know, you can't just buy a new TCM, you have to replace the whole Mechatronics unit which has a cost price of around $4100, so I guess we want to be sure we have done all the low-cost items first, before leaping to this.

Seeking any other ideas on this, or particularly any insights into seeing wandering voltages like this occur and what could cause that...

At this point I feel the only option left is replace the mech which is quite expensive... perhaps I should get a 2nd hand mech, however it's likely it will have it's own issues

I know on the older mechatronics units/TCM's that internal repairs are now being done by workshops where solder joints failed, wondering if this could be a thing on the DQ500.

Open for any ideas and thoughts, many thanks in advance!!



Codes listed below from VCDS:
Code:
Address 02: Auto Trans (J743)       Labels:. 0BH-927-711.clb
   Part No SW: 0BT 300 045 P    HW: 0BH 927 711 C
   Component: DSG DQ500-7F  H07 2302  
   Revision: 00H07V01    CVN: D80E7252
   Coding: 0014


10810 - Function Restricted due to Insufficient Voltage 
          U1400 00 [00101100] - -


10821 - System Voltage 
          P0562 00 [00101100] - Too Low


10907 - Main Pressure Valve 
          P179C 00 [00101100] - Electrical Malfunction


10906 - Cooling Oil Valve 
          P179D 00 [00101111] - Electrical Malfunction


                Address 02: Auto Trans  (0BT 300 045 P)


10:02:29
  IDE00018   Voltage terminal 15 14.2 V
  IDE00019   Voltage terminal 30 4.9 V