Gearbox Fault Codes

Right, have had her plugged in today because i'm getting gearbox fault message on the dash and gearbox goes into safe mode locked in third. When the ignition is turned on there are the gears displayed on the dash as normal and you can cylce through the lot with the gear lever, and sport button works high-low box all indicated on the dash, then turn the key to start and the gear is still displayed until the instant the engine fires when "gearbox fault" is displayed and the indicator on the dash of the gear disappears and the box is locked in third or reverse.

There were no fault codes logged on the gearbox but elsewhere there is a P1777 (gearbox ignition retard request line fault (driving cycle B)) and a P1775 (gearbox has signalled a fault condition to the ECM (driving cycle B)... i've checked every connector right through the gearbox harness, all were fine but i've cleaned them all anyway, the fusebox has been stripped and cleaned, the connections to the ecu have been cleaned but were fine anyway, the oil and filter in the gearbox have just been changed but the fault showed before that, I'm running out of ideas now...
I've took the crank position sensor off and cleaned that and though it seemed ok, possibly it could have packed in and be the cause of the P1777?
I'm sure this is going to turn out to be something rediculously simple like a short or a dodgy connection, am praying theres no uwanted gremlins in the ECM!
Any ideas what i should do next?

I suppose that your battery and alternator are good? Cos gearbox fault is a common message with low battery voltage. Check battery terminals, and all earth connections.
Probably also worth checking the engine compartment fuse box for signs of heating.

Thanks for your help, I thought the same but the code first showed up two days after I put a brand new battery on, I've tried taking it off and putting the old one back on but makes no difference... So I must've disturbed something when I fitted it, the alternator is brand new aswell, replaced that about September time... I'll check all the earths, I've got a crank position sensor on order, apparently that's not working

I had the same and spent ages going through everything it was the cable from the starter to the alternator that was corroded internally and the alt was only giving 11.8 volts as it goes past the starter on its way to the battery worth a look sorry cant be more help

so the corroded starter cable shows up a gearbox fault? I'll check that, that kindof makes sense because the starter has started not working randomly, i thought it needed changing but possibly a bad connection like you say
thankyou very much for your help

the alt sends its power to the battery via the starter so the cable from the starter to the battery has a bearing on how much of the alt output gets to the battery mine started with the intermittent starter problem took me ages to sort it out in the end got a new cable for a fiver and left the original in place also on the back of the starter there are two connections make sure they are both tight and if one stud feels loose take the wires off and it will tighten dont do as i did think terminal is knackered and bought a new starter fitted it and then found out that two turns and the loose terminal was sorted good luck hope it sorts it for you