Hi, it’s Glenn here. I can help you with your question.
As you probably already know, the TCM (transmission computer) gets signals from the gear lever position switch, the coolant temp sensors, the vehicle speed sensor and the throttle position sensor, which signal the computer that shifts solenoids inside the transmission to shift the gears. If one of these signals is missing then you will have a limp mode condition.
Your starting point really is a fault code read of the TCM, I'm thinking that you may have an intermittent fault with the gear lever position (inhibitor) switch, that may explain no light in the gear shift lever.
Yes a Nissan dealer does have the gear to plug in but a transmission specialist would be my recommendation, and I would suggest using a member of the Automatic Transmission Rebuilders of Australasia (ATRA). ATRA is a division of the Institute of Automotive Mechanical Engineers (IAME) and brings together a professional highly skilled and dedicated group of Transmission Repairers in Australia and New Zealand. Go to: http://www.atraonline.com.au & click on member lists to find someone close to you. Don't forget that if you have any more questions or you are unsure of what I mean in the information provided please ask for more clarification, I'm only too happy to work with you to achieve a good result. Cheers Glenn.