1998 XK8, 125k, transmission rebuilt at 110k. Over the last 500 miles or so of driving, I started receiving high gearbox temperature warnings. They were intermittent at first, but have become more persistent the more I drive, accompanied by sometimes erratic shifting. Codes are P0710 Transmission Fluid Temperature Sensor A Circuit, the ubiquitous P1000, and P1797 Neutral Switch Circuit Malfunction. After doing some research I cleaned the connector on the outside of the transmission, which made no difference. I found multiple people on the forum with identical issues that replaced the transmission internal wiring harness (LNC3380AA) and the problem went away for good. Is there anything else I should check before replacing this harness, and the associated fluid/filter change that comes along with dropping the pan?

 

I had a few XK8 and XJ8 ZF5HP24 gearboxes with 'HIGH GEARBOX TEMP' faults in the early 2000s when I worked at the dealer.

A new internal harness with integral temp sensor was installed and that fixed the problem.