I have been having nothing but problems with this issue. The transmission is in limp mode, with flashing M and S lights. I've checked the battery and replaced the alternator with a bosch reman. I have 14.40 volts with no load and 14.18 w/ loads.
The Rover was flooded at one point and time, but the thing has run fine for a number of years. I took the TCU out and did find a very small amount of corrosion on the board. I cleaned the TCU w/ cleaner and a brush, then reinstalled. When I fired it up the lights were gone and it ran/drove fine. I took it to work and when I went to leave for the day the transmission was in limp mode again. I have checked grounds, voltage, etc. The "Service Engine Soon" light was on, so I put a scanner on it. It's throwing 1 transmission code - P0758 which is a shift solenoid. I find it extremely unlikely that there is anything wrong with the transmission, as it was running perfectly before limp mode came back.

Is there any way to test the TCU at home? Is it possible to check the leads on the TCU for voltage to determine if it's functional or not?
I have put a volt meter on a few and there are only 2-3 that actually have 13.7-14.4 volts.

 

OK, so I was reminded that the rave manual has the diagram for the TCM... I got the volt meter out and went to town.

The XYZ pins have voltage when the gear selector is run through all the gears (P,D,1,2,3,N). so can't be the XYZ switch.

The pins for transmission high/low switch, battery power supply, battery output, Ignition power, and gearbox output shaft speed sensor, negative are putting out 12-13.8 volts. In a nutshell, I'm pretty sure all the input voltage is correct. The only thing I'm unsure of is the CAN, HIGH input/output pin is at 0 voltage, but for all I know that pin only gets voltage when the vehicle is driving, kicking into overdrive, or something like that...

Now what makes me think the TCM is bad is the fact that nearly all of my output pins are either reading 0.00 - 0.20. I checked all of the shift control solenoid pins (Pins #30,32,33, and 53) and they are all 0. I checked them with the truck running in park and then checked them while going through all the gears. no change in voltage at all, they all read 0. I don't know if the truck is supposed to be driving for those pins to have power though.

Also, I took out my TCU and cleaned it with electrical cleaner and a tooth brush again. when I put it back in limp mode was off and my service engine soon light shut off. I drove it around a little bit, but it was still in limp mode. When I parked it and turned it back on limp mode was back and the service engine soon light was back.

Any help would be greatly appreciated.

thanks

 

I am of no help, just wanted to remind you that if you do replace the ECU, you must replace the BCU from the same donor vehicle or the engine won't start.

 

I'm thinking removing and cleaning the TCU is causing the system to turn off Limp Mode, kinda like erasing trouble codes. After driving for a moment, the original cause comes back, sending it back into limp mode. This makes me think that a Shift Solenoid could be the issue. It would need to go through shifting to catch that the solenoid did not engage correctly.

I've got a VW that has the same issues at times. Not constant yet, just occasionally. I replaced the Valve Body, but have since put 45k miles on it which is the normal failure mileage for these valve bodies, so probably looking at another $800 for another valve body.

Also, on THIS PAGE, notice the possible causes. Maybe check them all.

Here's another helpful page. I am now suspecting an electrical issue, like a loose or shorted wire leading to the solenoid, bad connector? Maybe water ingress?

Going to check the wiring harness on the VW next...

 

Oh wow.. I thought I could just flash the TCU to this VIN number and I would be good to go. Looks like I Need a BCU as well? I am able to get a BCU and TCU from the same vehicle.

Super Sport that's actually a good point. I was thinking the solenoid would engage from R to D even though it was in limp mode. I have checked all the leads and what not, but I'll take a look at those links and go through the truck again.

I just can't justify taking this thing to the dealership when I could probably buy another Disco II for the cost of the bill.

 

In the VW there are a total of 5 solenoids. Each is used at varying times. It could be a single wire to a single solenoid. Or, the solenoid could be sticking. Low/Dirty Fluid?

I'm not sure if this is the correct valve body, but if so, it might help to trace the wires.
http://www.valvebodybuilders.com/lan...6e_2002up.html

 

The fluid was a little low when I checked before I started going through the electrical. I added some to see if that help, but didn't work. As for the cleanliness, it could be better, but its been worse. I think I am going to have to pull the pan to check wires at the solenoid later today, so I'll do a full service on it. my mechanic friend thinks it might be the solenoid, but he isn't sure. He is going to stop by today and help me take a look. Maybe your right about the solenoid SuperSport....

I will update when I have more information. And if anyone has any other ideas please let me know. I'm about to set fire to this thing and buy another DI. I knew I should have kept that 96 I had =)

 

I don't believe the transmission computer is synced to anything. It does store the vin and you can change it, but I've seen them with no vin stored from the factory.

The engine computer and BCU do sync security info.

 

Thanks Jafir. Worst case I could just get it synchronized at the dealership?

OK, me and the mechanic are pretty sure it's the TCU. He is at 80% and I'm more like 90%. We have the board striped from the case now and are testing all the resisters. most are at 20k ohms and one is at 100k ohms, meaning it's probably shorted out... we think.

Does anyone know if the the pins for MV1, MV2, MV3, MV4, and solenoid valves power supply are supposed to be hot or grounded? According to the diagram there is one hot that goes into the TCU, but what I can't figure out is if the pins that go from the TCU to the transmission solenoids are supposed to have 12volts or does the TCU send a ground signal?