Strange fault/no fault transfail safe 2005 TD6

Range rover l322 TD6 100,000 miles, throws transfail safe when driven in auto, live reading shows gear solenoid 2 always on, when driven in manual behaves perfectly and throws no fault. Mackies replaced gearbox about 10,000 miles ago, everyone is stumped, though I am personally leaning to an electrical problem being picked up by the ECU.
Tried a replacement transmission ECU got same message in auto, and no fault in manual, everything works high/low drive potentiometer is good, any help/ideas appreciated.

Problem solved by replacing transmission harness, cost £14 from GoS Axminster.

kubla said:

Problem solved by replacing transmission harness, cost £14 from GoS Axminster.

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What a result, had the harness been damaged some how during the gearbox change?

Mark Piercy said:

What a result, had the harness been damaged some how during the gearbox change?

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Original harness looked OK, however on testing with the bulb method after removing it, there was very obviously something intermittently wrong with the harness circuitry, decided to take one out of another vehicle and test, all was well, so had one delivered from GoS in two days. I could write a book about the times the stock "gearbox gubbed mate" has been opined, when it hasn't been, I always find it better to diagnose working towards the gearbox rather than away from it, hence we tried a transmission ECU first.
Hope this helps some chaps along the way, but obviously not a fix for everyone but worth the effort to test the original harness. Thanks for your interest.

It certainly does help knowing and could give someone the edge on an Intermittent problem

@kubla Thanks for sharing the outcome
So many get a fix but never think to share

gold rover said:

@kubla Thanks for sharing the outcome
So many get a fix but never think to share

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No problem glad to share. I can tell you of another “ gear box gubbed mate” that wasn’t. Lack of power wouldn’t go over 30mph but revved well and could select gears, used same fix as we used on Audis, blanked EGR with £20 blanking pipe, 10 minute fix and away she went good as new