Discovery TD5 - Autobox / Dashboard Lights - Strange Behaviour - Flashing "S" and "M"

Hi, unfortunately those OBDII codes are irrelevant as the D2 is not 100% compliant with that but for these intermittent limp mode symptoms if the XYZ switch was ruled out the most common problem is with chaffed gearbox harness at the P clip on the transfer box or loosen pins in the plug provided the fault codes are XYZ switch related, it can be an interruption in the wires which is not visible unless the harnes is completely removed and the wires exposed though it would be good to plug in a dedicated tester to see the exact fault codes cos it can be a valve block issue too or if the CAN fault code is still present it's a problem on that path between the engine ECU and gearbox ECU, that theory that the codes are the result of limp mode not vice-versa is not the best IMO, current codes retrieved with proper tester(not OBDII reader) will show where the problem is or at least will point to the involved circuit

a dedicated tester will give complete codes which have subcodes too for the specific circuit involved like in the attached tables(disregard that OBDII thing cos it's not correct) so come back when you have that kind of codes eventually find somebody with nanocom or hawkeye to help you

Intermittent faults in the electronic gear selection system on a d2 can be very difficult to diagnose as it takes only a fraction of a second disruption to the feed to the electronic automatic transmission ecu to cause the flashing m+s lights and limp mode and once engaged requires a complete shut down of ignition system before the fault will clear even if the cause of the fault has rectified itself.
That said there is a simple test you can do when the fault is present, preferably when the fault has just occured, but requires a dedicated d2 fault reader, nanocom, hawkeye or testbook and a copy of the table that shows the outputs from the xyz switch which can be found in automatic gear box section of rave the d2 work shop manual.
With the above fault readers you can access in both the bcu ( body control unit ) and eat (electronic automatic transmission) ecus , the outputs they receive from the xyz switch on the w,x,y,z tracks so as soon as the fault occurs, with the engine still running (do not turn off) plug in reader, go into bcu and eat and read and note down the outputs received from the xyz switch for each gear position and compare them with those in the table from rave.
Note, if you uses a nanocom you may need to reverse the wxyz axis on your table of readings for one of the ecus to get them to match.
Any discrepancy between the readings you have taken and the table in rave will indicate a fault in wiring circuit, if in both, between xyz switch and connector by handbrake, if I one only between this connector and relevant ecu.
In my case, similar to yours, developing over 18 months and getting more frequent, when I did this test, I got no feed from the xyz switch in any gear position to either ecu which led me conclude that the xyz switch was itself not receiving power input from the bcu.
The wxyz tracks in the xyz switch receive their power input on a dedicated circuit from the ignition switch through a switch in the bcu, so a fault in this circuit will not affect the normal operation of the bcu and as the bcu does not store fault codes cannot be found with diagnostic tool.
I eventually narrowed down the fault to the switch in the bcu being the culprit and with the aid of an auto electrician wired in a simple fix which worked well for several months until other failing in bcu lead me to replacing bcu.
If you do test and get same results as I did, post on here results and I will post fix I did.

Im not sure if this has been covered by anyone else as I haven't read all the replies. I've had the same problem a couple of times and have found a solution that worked both times. cant remember where I got the idea from but the solution was to check the main Ecu connectors (the red one in my case) for oil fouling which was effectively shorting the terminals. I got some electrical contact cleaner gave it a good clean up (there was for some inexplicable reason a lot of oil) and surprise surprise it did the trick.. Ive done the same bit of a clean up today as it happens and again a lot of oil in the connector.

Landchef said:

....(there was for some inexplicable reason a lot of oil)....

Click to expand...

that's not inexplicable at all, it's widely covered, just google out "Td5 oil at the ECU" and you'll find around 1 million of results so do what's needed and change the injector loom

Until you actually plug it in and see what diag says it could be anything our D2 had m +s flashing fault code came back as air in take temp to high......go figure.

Mind you it had sat 2 weeks not used I put it down to low battery voltage been OK since clearing the dtcs and giving it a decent drive

Just to offer some sort of update on this...

We replaced the XYZ switch, with a brand new gen item. When we drove her home from the mechanic's, it seemed to have fixed it. It lasted about a week, before it started happening again! I guess it wasn't the XYZ switch itself as a electronic unit that was specifically at fault.

She went back to the garage as she was still completely undriveable. She was there for 2-3 weeks as she hadn't been booked in, and sat around looking very sorry for herself. What's odd here, is that the battery was then allowed to go completely flat. By the time the mechanic jumped and then charged her back up, and started tying to diagnose the fault again - it had gone. He kept her for another week, and it didn't happen once for him.

We went back and collected the car, that was many months ago now - and touching all wood around me - it hasn't happened once to us since either. Perhaps, just perhaps, and if you're quite lucky, disconnecting the battery for a little while to allow all systems to go completely dead, might just help you out - it's different to the pulling over and restarting the car.

We never did get to the bottom of what the actual cause was. It's all pretty odd... We've decided to part with her now, whilst she's working. In the end, it was one too many electrical problems at a time when we really didn't need them. Well aware that this is part and parcel of Landy ownership - but it kind of grinds you down over a number of years. :-(