Member Since: 17 Jan 2019
Location: 44022
Posts: 9
No Communication with TCU after valve body replacement
I am having issues with an LR3 (USA spec vehicle)
transmission problem. I am getting involved after someone else already worked on it, which is frustrating as you can imagine. The truck originally would have a hard shift from 3-4 and would display "F" in the cluster. A key cycle would make the F go away and the problem would happen again. The previous owner swapped the valve body and transferred the TCU to the replacement unit. Now it displays "E" in the cluster and will not move. My GAP tool shows error code U0101-87 Lost Communication With transmission control module in multiple control units. The shifter moves freely through all positions, but the truck does not move. I checked the alignment of the shift rods and the slider on the TCU and everything is correct. The plug is fitted securely inside and out of the transmission case. I have searched this and other forums for clues but I am coming up short. It sure sounds like something happened during the swap, but I cannot figure out what it is. Any ideas?
5th Jan 2021 6:34 pm
Nutterwatts
Member Since: 12 Aug 2020
Location: Bristol
Posts: 57
There was a technical bulletin about troubleshooting multiple error codes, don't know if it will help!
Member Since: 17 Jan 2019
Location: 44022
Posts: 9
Thank you, I have seen this bulletin before. I like how they acknowledge the “complex nature of the vehicle.” An understatement if I ever heard one. If I cannot find something that wasn’t put back together right I will be going through wiring like the bulletin says. I am really thinking that something is out of place considering that it was different before it was worked on. But anything is possible.
6th Jan 2021 12:17 am
Nutterwatts
Member Since: 12 Aug 2020
Location: Bristol
Posts: 57
Do you have any other codes than 'U' ones? I was diagnosing a problem where it kept going into limp mode with the Christmas tree on the dash. A mixture of E's and F's on the display.
In the end I traced it to the mechatronic connector being corroded, once I had spliced a new one in everything worked
Can your diagnostic tool see the TCU and get error codes from it? just wondering if it's on the CANBUS network or not. There are about 14 units that all talk to one another if one goes down they end up going into safe mode. I read some previous comments the more it complains about the smaller the actual issue!
I take it you have tried a hard reset as well?
6th Jan 2021 1:00 am
LKSTK
Member Since: 17 Jan 2019
Location: 44022
Posts: 9
I should have mentioned before, the GAP diag tool is stating that the TCU is “not fitted.” It is off the CAN completely. Hard reset a few times, after each time checking connectors. There are codes in the Engine Control Unit: P0695-00 Fan control 3, and P0579-00 Speed Control Multifunction Input A - Circuit Range/Performance.
Where was the corrosion on yours? In the loom going to the transmission? Or on the inside?
6th Jan 2021 6:09 am
Nutterwatts
Member Since: 12 Aug 2020
Location: Bristol
Posts: 57
It was in the connector:
I thought one of the pins had been pushed back but on checking with a magnifying glass could see corrosion in it, when poking around with a needle I managed to get loose bits of rust out! obviously they were floating around in the plug causing all sorts of short circuits.
Have you checked the continuity of the CAN wires to the connector, the one for the TCU is a splice of the wire running past the rear wheel arch.
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